Heat-treating methods and systems

ABSTRACT

A method involves pre-heating a workpiece to an intermediate temperature, heating a surface of the workpiece to a desired temperature greater than the intermediate temperature, and enhancing cooling of the workpiece. Enhancing cooling may involve absorbing radiation thermally emitted by the workpiece. An apparatus includes a first heating source for heating a first surface of a semiconductor wafer, a second heating source for heating a second surface of the semiconductor wafer, and a first cooled window disposed between the first heating source and the semiconductor wafer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 09/729,747, filed Dec. 4, 2000, which is hereby incorporatedherein by reference. This application further claims priority fromPatent Cooperation Treaty application serial number PCT/CA01/00776,filed May 30, 2001, also incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to heating of objects, and moreparticularly to methods and systems for heat-treating a workpiece.

BACKGROUND OF THE INVENTION

Many applications require heating or annealing of an object orworkpiece. For example, in the manufacture of semiconductor chips suchas microprocessors, a semiconductor wafer, such as a silicon wafer, issubjected to an ion implantation process, which introduces impurityatoms or dopants into a surface region of a device side of the wafer.The ion implantation process damages the crystal lattice structure ofthe surface region of the wafer, and leaves the implanted dopant atomsin interstitial sites where they are electrically inactive. In order tomove the dopant atoms into substitutional sites in the lattice to renderthem electrically active, and to repair the damage to the crystallattice structure that occurs during ion implantation, it is necessaryto anneal the surface region of the device side of the wafer by heatingit to a high temperature.

Heating of a semiconductor wafer may be achieved by a number of distincttypes of methods, including the following:

-   (a) Adiabatic—where the energy is provided by a pulse energy source    (such as a laser, ion beam, electron beam) for a very short duration    such as 10 to 100 nanoseconds, for example. This high intensity,    short duration energy melts the surface of the semiconductor to a    depth of about one to two microns.-   (b) Thermal flux—where energy is provided for a longer duration,    such as two microseconds to five milliseconds. Thermal flux heating    creates a substantial temperature gradient extending much more than    two microns below the surface of the wafer, but does not cause    anything approaching uniform heating throughout the thickness of the    wafer.-   (c) Isothermal—where energy is applied for much longer duration,    such as 1 to 100 seconds for example, so as to cause the temperature    of the wafer to be substantially uniform throughout its thickness at    any given region.

The high temperatures required to anneal the device side of asemiconductor wafer tend to produce undesirable effects using existingtechnologies. For example, diffusion of the dopant atoms deeper into thesilicon wafer tends to occur at much higher rates at high temperatures,with most of the diffusion occurring within close proximity to the highannealing temperature required to activate the dopants. As performancedemands of semiconductor wafers increase and device sizes decrease, itis necessary to produce increasingly shallow and abruptly definedjunctions, and therefore, diffusion depths that would have beenconsidered negligible in the past or that are tolerable today will nolonger be tolerable in the next few years or thereafter. Currentindustry roadmaps, such as the International Technology Roadmap forSemiconductors 1999 Edition (publicly available athttp://public.itrs.net/) indicate that doping and annealing technologieswill have to produce junction depths as shallow as 30 nm by 2005, and asshallow as 20 nm by 2008.

Existing annealing technologies are generally incapable of achievingsuch shallow junction depths. For example, one existing rapid thermalannealing method involves illuminating the device side of the wafer withan array of tungsten filament lamps in a reflective chamber, to heat thewafer at a high rate. However, the wafer tends to remain hot for aconsiderable time after the power supply to the tungsten filaments isshut off, for a number of reasons. Typical tungsten lamps have arelatively long time constant, such as 0.3 seconds, for example, as aresult of the high thermal masses of the filaments, which remain hot andcontinue to irradiate the wafer after the power supply to the filamentsis discontinued. This slow time response of the filaments gives rise tothe dominant thermal lag in such a system. Also, radiation return fromthe walls of the reflective process chamber provides another source ofcontinued heating after the power is shut off. A temperature versus timeprofile of the wafer using this tungsten lamp annealing method tends tohave a rounded top with relatively slow cooling after the power to thefilaments is discontinued. Accordingly, if the wafer is heated with sucha system to a sufficiently high temperature to repair the crystallattice structure and activate the dopants, the wafer tends to remaintoo hot for too long a period of time, resulting in diffusion of thedopants to significantly greater depths in the wafer than the maximumtolerable diffusion depths that will be required to produce 30 nmjunction depths.

Although the vast majority of dopant diffusion occurs in the highesttemperature range of the annealing cycle, lowering the annealingtemperature is not a satisfactory solution to the diffusion problem, aslower annealing temperatures result in significantly less activation ofthe dopants and therefore higher sheet resistance of the wafer, whichwould exceed current and/or future tolerable sheet resistance limits foradvanced processing devices.

One annealing method that has achieved some success in producing shallowjunctions involves the use of lasers to heat and anneal the device sideof the wafer. The short-wavelength monochromatic radiation produced bylasers, such as excimer lasers for example, tends to be absorbed at veryshallow depths in the device side of the wafer, and the short duration,high-power laser pulse (for example, a 10 nanosecond pulse deliveringabout 0.4 J/cm² to the device side surface) typically used for thisprocess tends to heat a small localized area of the surface of thedevice side to melting or near-melting temperatures very rapidly, insignificantly less than the time required for significant thermalconduction in the wafer. Accordingly, the bulk regions of the wafersubstrate tend to remain cold and therefore act as a heat sink for theheated surface region, causing the surface region to cool very quickly.A typical surface temperature versus time profile of the localized areaof the device side surface using laser annealing tends to betriangular-shaped and steeply sloped for both the heating and coolingstages and therefore, the device side spends only a very short period oftime at high temperatures. Thus, the wafer does not remain hot longenough for much dopant diffusion to occur. However, because the bulkregions of the wafer, as well as device side areas other than thelocalized area heated by the laser, remain cold when the localizedsurface area of the device side is heated to annealing temperature,extreme thermal gradients are produced in the wafer, resulting in largemechanical strains which cause the crystal planes within the wafer toslip, thereby damaging or breaking the crystal lattice. In this regard,a very small spatial movement may completely destroy the crystallattice. Thermal gradients may also cause other damage, such as warpageor defect generation.

Even in the absence of slippage, a non-uniform temperature distributionacross the wafer may cause non-uniform performance-relatedcharacteristics, resulting in either inadequate performance of theparticular wafer, or undesirable performance differences from wafer towafer. In addition, the large amount of energy delivered by the laser orlasers to the device side of the wafer is non-uniformly absorbed by thepattern of devices thereon, resulting in deleterious heating effects inregions of the wafer where annealing is not desired, and may alsoproduce further large temperature gradients causing additional damage tothe silicon lattice.

Other ultra-fast adiabatic heating methods similar to laser annealinghave also been attempted. For example, flash lamps and microwave pulsegenerators have been used to rapidly heat the device side of the waferto annealing temperature, resulting in a temperature-time profilesimilar to that achieved by laser annealing, with similar disadvantages.

At least one approach in the early 1990s involved a low-temperatureannealing stage followed by a laser annealing stage. The low-temperaturestage typically involved heating the wafer to a mid-range temperature inan electric furnace, such as 600° C. for example, for a relatively longperiod of time, such as an hour or longer. A typical temperature-timeprofile of the device side surface using this method is flat for a verylong time, followed by a rapid increase and rapid cooling of the surfaceresulting from the laser anneal. Although this method purports to reducejunction leakage currents as compared to laser annealing alone, the longduration of the low-temperature annealing stage causes the dopants todiffuse to greater depths within the device side of the wafer. Suchdiffusion, which may have been tolerable or perhaps even negligible byearly 1990s standards, would not permit the formation of sufficientlyshallow junctions to comply with current performance and industryroadmap requirements.

A more recent approach involves the use of a fast responding argonplasma arc lamp heat source to irradiate the substrate side of thewafer, to rapidly heat the entire wafer to annealing temperatures. Thetime response of the arc lamp is short (typically on the order of 0.1milliseconds or less) compared to that of the wafer itself, and thus thedominant thermal lag is that of the wafer, in contrast with the tungstenlamp method above, where the dominant thermal lag is that of thetungsten filaments. A typical temperature-time profile of the waferusing this method tends to have heating and cooling temperature ratesthat are intermediate between those of tungsten systems and laserannealing systems. Thus, the wafer spends less time at the highannealing temperature and therefore, less dopant diffusion occurs thanwith the tungsten lamp method. Accordingly, this method is capable ofproducing much shallower junction depths than tungsten lamp systems. Asthe entire wafer is heated rather than just the device side surface, theextreme transverse thermal gradients that result in laser annealing areavoided, thereby minimizing additional damage to the crystal lattice. Inaddition, as the substrate side is irradiated rather than the deviceside, non-uniform heating of the device side due to non-uniformabsorption by the pattern of devices is also much lower than for laserannealing, resulting in lower lateral temperature gradients and reduceddamage to devices. However, early indications suggest that embodimentsof this method may result in somewhat deeper diffusion of the dopantsthan laser annealing.

An older approach, dating back to the 1980s, involved heating asemiconductor wafer by combining isothermal heating and thermal fluxheating. The entire wafer was heated to a first intermediate temperaturevia isothermal heating with continuous wave lamps. Then, the front sideof the wafer was heated via thermal flux using a high-power pulsed lamparray. These heating methods were carried out while the wafer andheating sources were held within an integrating light pipe orkaleidoscope with reflective inner surfaces that reflect and re-reflectradiant energy toward the wafer. Thus, as the wafer began to coolfollowing deactivation of the lamps, radiation thermally emitted by thewafer would be reflected back to the wafer where it would bere-absorbed, thereby heating the wafer, and effectively slowing itscooling. This caused the wafer to spend longer times at hightemperatures, thereby tending to increase dopant diffusion to depthsthat would be unacceptable by modern standards. In addition, there-reflections of such radiation back to the wafer tended to producenon-uniform heating in the wafer, resulting in slippage and otherproblems associated with non-uniform or excessive heating. Moreover,this method purported to be suitable for heating the wafer with 2%uniformity, which is not acceptable for modern RTP systems. In addition,this method typically involved a delay of a few seconds between theisothermal heating stage and the subsequent thermal flux heating stage,during which the wafer remained at a relatively high intermediatetemperature, such as 1100° C., for example. This delay at theintermediate temperature can cause significant dopant diffusion, thusinterfering with the ability to produce shallow junctions in accordancewith modern performance requirements.

Accordingly, there is a need for improved methods and systems forheat-treating a workpiece, such as a semiconductor wafer. In addition toannealing a semiconductor wafer for ion activation and lattice repairpurposes, other applications may also benefit from an improvedheat-treating method that addresses the above problems.

SUMMARY OF THE INVENTION

The present invention addresses the above needs by providing, inaccordance with one aspect of the invention, a method and system forheat-treating a workpiece. The method includes pre-heating the workpieceto an intermediate temperature, heating a surface of the workpiece to adesired temperature greater than the intermediate temperature, andenhancing cooling of the workpiece. Pre-heating the workpiece to theintermediate temperature, prior to heating the surface to the higherdesired temperature, decreases the magnitude of the thermal gradientsthat occur in the workpiece when the surface is heated to the desiredtemperature. Therefore, thermal stress in the workpiece is reduced.Where the workpiece has a crystal lattice structure, such as asemiconductor wafer for example, damage to the lattice iscorrespondingly reduced.

In addition, heating the surface of the workpiece to the desiredtemperature, as opposed to heating the entire workpiece to the desiredtemperature, results in much faster cooling of the surface, as thecomparatively colder bulk or body of the workpiece may act as a heatsink to cool the surface by conduction. Where the workpiece is adopant-implanted semiconductor wafer for example, this faster coolingresults in shallower dopant diffusion, allowing for the formation ofshallower junctions in accordance with modern and future industryrequirements.

Enhancing cooling of the workpiece further reduces the time that theworkpiece spends at high temperatures. In embodiments where theworkpiece is a semiconductor wafer, this faster cooling again reducesdopant diffusion in the workpiece, allowing for the formation ofshallower junctions.

Enhancing cooling preferably includes absorbing radiation thermallyemitted by the workpiece. Thus, radiation thermally emitted by theworkpiece is absorbed, rather than being reflected back to the workpieceto effectively re-heat it.

Absorbing may include absorbing the radiation at a radiation absorbingsurface. Such a surface may include a wall of a radiation absorbingchamber, for example.

Alternatively, or in addition, absorbing may include absorbing theradiation thermally emitted by the workpiece at a selective-filteringsystem. If so, then pre-heating the workpiece may involve transmittingradiation produced by an irradiance source through a filtering device ofthe selective-filtering system to the workpiece. Transmitting mayinvolve transmitting the radiation to a second surface of the workpiece.

Similarly, heating the surface of the workpiece may include transmittingradiation produced by an irradiance source through a filtering device ofthe selective-filtering system to the surface of the workpiece.

The method may further include cooling the selective-filtering system.This may be achieved by causing a liquid to flow across a surface of awindow of the selective-filtering system, for example. Moreparticularly, this may include causing a liquid to flow in a spacedefined between first and second spaced apart windows of theselective-filtering system.

Heating the surface may include rapidly heating the surface to thedesired temperature by activating a source of thermal flux or adiabaticenergy. The method may further include deactivating the source ofthermal flux or adiabatic energy.

Pre-heating the workpiece to the intermediate temperature may includepre-heating the workpiece to a temperature in the range of 600° C. to1250° C. Heating the surface of the workpiece to the desired temperaturemay include heating the surface to a temperature in the range of 1050°C. to 1430° C. These temperatures may be particularly advantageous inembodiments where the workpiece is a silicon semiconductor wafer, forexample, as the upper end of the desired temperature range correspondsroughly to the melting point of silicon. These temperature ranges mayvary for semiconductor wafers made from materials other than silicon.

Pre-heating the workpiece preferably includes pre-heating the workpiecefor a time period greater than a thermal conduction time of theworkpiece. This serves to allow much of the energy supplied to theworkpiece during the pre-heating stage to conduct through the workpiece,thereby raising substantially the entire bulk of the workpiece to theintermediate temperature.

Conversely, heating preferably involves heating the surface for a timeperiod less than a thermal conduction time of the workpiece. Thus, thesurface may be heated quickly to the desired temperature while the bulkof the workpiece remains substantially at the cooler intermediatetemperature. This allows the bulk of the workpiece to act as a heat sinkfor the heated surface, causing the surface to cool much more rapidlywhen the heating stage is completed. As dopant diffusion occurs moresignificantly at the highest temperature range, i.e. between theintermediate temperature and the desired temperature, this approachminimizes the time spent by the surface in this highest temperaturerange, thereby minimizing dopant diffusion.

Heating the surface of the workpiece may include commencing the heatingsubstantially immediately when the workpiece reaches the intermediatetemperature. For example, this may include commencing the heating of thesurface within an interval following the arrival of the workpiece at theintermediate temperature, the interval having a duration less than orequal to a thermal conduction time of the workpiece. This avoids anysubstantial delay at the intermediate temperature, which, in embodimentswhere the workpiece is a semiconductor wafer, avoids any correspondingincrease in dopant diffusion that would otherwise result from such adelay.

Pre-heating may include pre-heating the workpiece at a rate of at least100° C. per second, preferably at a rate of at least 400° C. per second.Pre-heating may include irradiating the workpiece with electromagneticradiation produced by an arc lamp. If desired, more than one such arclamp may be employed, such as an array of arc lamps, for example.

Heating may include irradiating the workpiece with electromagneticradiation produced by a flash lamp. This may include a plurality of suchflash lamps, if desired.

In embodiments where the workpiece is a semiconductor wafer, the heatingis preferably carried out at a rate of at least 10,000° C. per second,or even more preferably at a rate of at least 100,000° C. per second.The heating is preferably achieved by irradiating the workpiece withelectromagnetic radiation produced by an arc lamp or a flash lamp. Thismay include use of an array of such lamps. Alternatively, other heatingdevices, such as a laser, may be substituted if desired.

Enhancing cooling of the workpiece preferably includes allowing theworkpiece to cool at a rate of at least about 100° C. per second,preferably at a rate of at least 150 to 180° C. per second.

In accordance with another aspect of the invention, there is provided asystem for heat-treating a workpiece. The system includes a pre-heatingdevice operable to pre-heat the workpiece to an intermediatetemperature, a heating device operable to heat a surface of theworkpiece to a desired temperature greater than the intermediatetemperature, and a cooling enhancement system for enhancing cooling ofthe workpiece to a temperature below the intermediate temperature.

The cooling enhancement system preferably includes an absorption systemoperable to absorb radiation thermally emitted by the workpiece.

The absorption system may include a radiation absorbing surface. Theradiation absorbing surface may include a wall of a radiation absorbingchamber.

The absorption system may include a selective-filtering system. If so,the selective-filtering system may include a filtering device interposedbetween the pre-heating device and the workpiece and configured totransmit radiation produced by the pre-heating device to the workpiece.In this regard, the filtering device may be configured to transmit theradiation to a second surface of the workpiece.

Similarly, the selective-filtering system may include a filtering deviceinterposed between the heating device and the workpiece and configuredto transmit radiation produced by the heating device to the surface ofthe workpiece.

The system may further include a cooling subsystem for cooling theselective-filtering system.

The selective-filtering system may include at least one window, and thecooling subsystem may include a liquid-cooling subsystem for causing aliquid to flow across a surface of the window.

The selective-filtering system may include first and second spaced apartwindows, and the cooling subsystem may include a liquid-coolingsubsystem for causing a liquid to flow in a space defined between thewindows.

The heating device may include a source of thermal flux or adiabaticenergy operable to rapidly heat the surface to the desired temperature.

The pre-heating device may be operable to pre-heat the workpiece to atemperature in the range of 600° C. to 1250° C., and similarly, theheating device may be operable to heat the surface to a temperature inthe range of 1050° C. to 1430° C.

The pre-heating device is preferably operable to pre-heat the workpiecefor a time period greater than a thermal conduction time of theworkpiece.

Conversely, the heating device is preferably operable to heat thesurface of the workpiece for a time period less than a thermalconduction time of the workpiece. The heating device is preferablyoperable to commence heating the surface substantially immediately whenthe workpiece reaches the intermediate temperature.

The pre-heating device may be operable to pre-heat the workpiece at arate of at least 100° C. per second. The pre-heating device may includean arc lamp operable to irradiate the workpiece with electromagneticradiation.

The heating device may include a flash lamp operable to irradiate theworkpiece with electromagnetic radiation.

The cooling enhancement system preferably allows the workpiece to coolat a rate of at least about 100° C. per second.

In accordance with another aspect of the invention, there is provided asystem for heat-treating a workpiece. The system includes means forpre-heating the workpiece to an intermediate temperature, means forheating a surface of the workpiece to a desired temperature greater thanthe intermediate temperature, and means for enhancing cooling of theworkpiece. The means for enhancing preferably includes means forabsorbing radiation thermally emitted by the workpiece.

In accordance with another aspect of the invention, there is provided aselective-filtering system for use in heat-treating a workpiece. Thesystem includes a first filtering device configured to transmitradiation from a pre-heating device to the workpiece to pre-heat theworkpiece to an intermediate temperature, and configured to absorbradiation thermally emitted by the workpiece. The system furtherincludes a second filtering device configured to transmit radiation froma heating device to a surface of the workpiece to heat the surface to adesired temperature greater than the intermediate temperature, andconfigured to absorb radiation thermally emitted by the workpiece.

The system may further include a cooling subsystem for cooling the firstand second filtering devices.

If desired, at least one of the first and second filtering devices mayinclude a liquid-cooled window. The liquid-cooled window may include awater-cooled quartz window.

In accordance with another aspect of the invention, there is provided amethod of heat-treating a workpiece. The method includes pre-heating theworkpiece to an intermediate temperature, and heating a surface of theworkpiece to a desired temperature greater than the intermediatetemperature, the heating commencing substantially immediately when theworkpiece reaches the intermediate temperature. Commencing the surfaceheating substantially immediately when the workpiece reaches theintermediate temperature avoids any delay at the intermediatetemperature, which, in embodiments where the workpiece is asemiconductor wafer, avoids any corresponding increase in dopantdiffusion that would otherwise result from such a delay.

Heating the surface preferably includes commencing the heating withinless than one second after the workpiece reaches the intermediatetemperature. This preferably includes commencing the heating within lessthan one-quarter second after the workpiece reaches the intermediatetemperature. More preferably still, this may include commencing theheating within less than 1×10² milliseconds after the workpiece reachesthe intermediate temperature. This may include commencing the heatingwithin less than 1×10¹ milliseconds after the workpiece reaches theintermediate temperature.

Pre-heating preferably includes pre-heating the workpiece for a timeperiod greater than a thermal conduction time of the workpiece.Conversely, heating preferably includes heating the surface for a timeperiod less than a thermal conduction time of the workpiece.

Heating may include commencing the heating in response to an indicationthat the temperature of the workpiece is at least the intermediatetemperature. The method may further include producing the indication.

Pre-heating preferably includes irradiating the workpiece. This mayinclude exposing the workpiece to electromagnetic radiation produced byan arc lamp. Alternatively, or in addition, this may include exposingthe workpiece to electromagnetic radiation produced by at least onefilament lamp.

Pre-heating preferably includes pre-heating the workpiece at a rate ofat least 100° C. per second. This may include pre-heating the workpieceat a rate of at least 400° C. per second.

Heating the surface of the workpiece preferably includes irradiating thesurface. This may include exposing the surface to electromagneticradiation produced by a flash lamp. Alternatively, this may includemoving a laser beam across the surface.

The method may further include absorbing radiation reflected andthermally emitted by the workpiece. Absorbing may include absorbing theradiation in a radiation absorbing environment. This may includeabsorbing the radiation in at least one radiation absorbing surface.

The method may further include cooling the at least one radiationabsorbing surface.

In accordance with another aspect of the invention, there is provided asystem for heat-treating a workpiece. The system includes a pre-heatingdevice operable to pre-heat the workpiece to an intermediatetemperature, and a heating device operable to heat a surface of theworkpiece to a desired temperature greater than the intermediatetemperature, and operable to commence the heating of the surfacesubstantially immediately when the workpiece reaches the intermediatetemperature.

The heating device and the pre-heating device may be operable to carryout the various methods described above and elsewhere herein.

The system may further include a temperature indicator operable toproduce an indication of a temperature of the workpiece, in which casethe heating device may be operable to commence the heating in responseto an indication from the temperature indicator that the temperature ofthe workpiece is at least the intermediate temperature.

The pre-heating device may include means for irradiating the workpiece.The pre-heating device may include an irradiance source operable toirradiate the workpiece. The irradiance source may includes an arc lamp.Or, the irradiance source may include at least one filament lamp.Alternatively, the pre-heating device may include a hot body locatableto pre-heat the workpiece.

The heating device may include means for irradiating the surface. Theheating device may include an irradiance source operable to irradiatethe surface. The irradiance source may include a flash lamp.Alternatively, the irradiance source may include a laser.

The system may further include a radiation absorbing environmentoperable to absorb radiation reflected and thermally emitted by theworkpiece. Similarly, the system may further include at least oneradiation absorbing surface operable to absorb radiation reflected andthermally emitted by the workpiece. The system may further include acooling subsystem operable to cool the at least one radiation absorbingsurface.

In accordance with another aspect of the invention, there is provided asystem for heat-treating a workpiece. The system includes means forpre-heating the workpiece to an intermediate temperature, and means forheating a surface of the workpiece to a desired temperature greater thanthe intermediate temperature, including means for commencing the heatingsubstantially immediately when the workpiece reaches the intermediatetemperature.

In accordance with another aspect of the invention, there is provided asemiconductor heating apparatus. The apparatus includes a first heatingsource for heating a first surface of a semiconductor wafer, and asecond heating source for heating a second surface of the semiconductorwafer. The apparatus further includes a first cooled window disposedbetween the first heating source and the semiconductor wafer.

The first cooled window may include a first optically transparent platecooled by a cooling fluid. The first cooled window may further include asecond optically transparent plate separated from the first opticallytransparent plate to define a passageway through which the cooling fluidmay flow.

The cooling fluid may include water.

The first optically transparent plate may be formed from quartz, as maybe the second optically transparent plate.

The semiconductor heating apparatus may further include a second cooledwindow disposed between the second heating source and the semiconductorwafer.

The first cooled window preferably absorbs radiation thermally emittedby the semiconductor wafer. In this regard, the first cooled windowpreferably absorbs radiation to controllably cool the semiconductorwafer at a rate of at least 100° C. per second.

The second cooled window may absorb radiation to controllably cool thesemiconductor wafer at a rate of at least 100° C. per second.

The first heating source may include an arc lamp. This may include anarray of arc lamps if desired. Similarly, the second heating source mayinclude an arc lamp, which may include an array of arc lamps if desired.

Or, the first heating source may include a tungsten lamp or array oftungsten lamps.

The semiconductor heating apparatus may further include a chamberhousing the semiconductor wafer, wherein the chamber has one or morewalls with a radiation-absorbing surface.

Alternatively, the apparatus may include a chamber housing thesemiconductor wafer, wherein the chamber has one or more walls with aradiation-reflecting surface. If so, the chamber walls may be inwardlytapered at an angle from 2 to 6 degrees from perpendicular.

If desired, the enhanced cooling of the bulk of the workpiece may becarried out by absorbing radiation reflected by or thermally emitted bythe workpiece. In one exemplary embodiment, the workpiece is isolatedfrom a heating source by a cooled window and radiation thermally emittedby the workpiece is absorbed by the cooled window. In anotherembodiment, the workpiece is held within a radiation absorbing chamberand radiation reflected by or thermally emitted by the workpiece isabsorbed by one or more walls of the chamber. Further embodimentscombine one or more such cooled windows with such a radiation absorbingchamber.

If a cooled window is used, the cooled window may include a firstoptically transparent plate that is cooled by flow of a cooling fluid.The cooled window may further include a second optically transparentplate spaced apart from the first optically transparent plate to defineat least one channel between the first and second optically transparentplates, and the cooling fluid may be pumped through that channel. Theoptically transparent plates may be formed from a material generallytransparent to the radiant energy emitted by the radiant sources used toheat the workpiece. One such optically transparent material to form theoptically transparent plate is quartz, although sapphire, glass or othermaterials may be substitutable depending upon the heating devices used.The cooling fluid may include a liquid, such as water. In oneembodiment, the cooled window absorbs radiation with wavelengths ofabout 1.4 μm and above, which are the radiant wavelengths where most ofthe radiation is expected to be emitted by a workpiece such as a siliconsemiconductor wafer.

A semiconductor heating apparatus according to one embodiment of theinvention includes a first heating source for heating a first surface ofthe semiconductor wafer, and a second heating source for heating asecond surface of the semiconductor wafer, with a first cooled windowdisposed between the first heating source and the semiconductor wafer;and a second cooled window disposed between the second heating sourceand the semiconductor wafer. The cooled windows isolate the heatingsources from the semiconductor wafer to prevent contamination. Inaddition, the cooled windows act to controllably cool the wafer byabsorbing radiation thermally emitted by or reflected by the wafer.Preferably, the cooled windows absorb radiation at a rate high enough toachieve a cooling rate of 150 to 180° C. per second to controllably coolthe semiconductor wafer.

Preferably, the first cooled window includes a first opticallytransparent plate cooled by a cooling fluid. Most preferably, the firstcooled window further includes a second optically transparent plateseparated from the first optically transparent plate to define at leastone passageway or channel through which the cooling fluid may flow. Thepreferred cooling fluid is a liquid such as water. The preferredmaterial for forming the optically transparent plates is quartz.

In some exemplary embodiments the first and second heating sources arearc lamps or arrays of arc lamps. Either one of the first and secondheating sources may also be a tungsten lamp or array of tungsten lamps.

One embodiment has one or more chambers for housing the semiconductorwafer during heat-treating, wherein the chambers have sidewalls withradiation reflecting surfaces. However, the semiconductor heatingapparatus may further include a chamber for housing the semiconductorwafer, wherein the chamber has one or more sidewalls withradiation-absorbing surfaces. The radiation-absorbing surfaces furtherassist in controllably cooling the semiconductor wafer.

In embodiments where the workpiece is a semiconductor wafer for example,pre-heating the workpiece may include irradiating a substrate side ofthe wafer, and heating the surface of the workpiece may includeirradiating a device side of the wafer. Due to the greater uniformity ofthe emissivity across the substrate side of the wafer as compared to thedevice side, the irradiation of the substrate side to pre-heat the waferresults in significantly greater temperature uniformity in the wafer,and therefore significantly less thermal stress damage, than othermethods that deliver the entire annealing energy to the device side ofthe wafer. In contrast, if the device side alone was irradiated to heatthe device side from room temperature to 1050° C. for example, then anemissivity difference of 10% between different devices on the deviceside may result in a lateral temperature difference of approximately100° C., which is well in excess of current tolerable temperaturedifference limits, and may therefore cause thermal stress damage to thedevices and to the lattice.

Other aspects and features of the present invention will become apparentto those ordinarily skilled in the art upon review of the followingdescription of specific embodiments of the invention in conjunction withthe accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

In drawings which illustrate embodiments of the invention,

FIG. 1 is a block diagram of a system for heat-treating a workpieceaccording to a first embodiment of the invention;

FIG. 2 is a schematic side view of a system for heat-treating aworkpiece according to a second embodiment of the invention (shown witha side wall removed);

FIG. 2A is a cross-sectional view in side elevation of a heating deviceand a filtering device of the heat-treating system shown in FIG. 2;

FIG. 3 is a flowchart of a heat-treating routine executed by a processorcircuit of the system shown in FIG. 2;

FIG. 4 is a graphical representation of a temperature-time profile of asurface of the workpiece shown in FIG. 2 during a thermal cycleaccording to the second embodiment of the invention;

FIG. 5 is a schematic side view of a system for heat-treating aworkpiece according to a third embodiment of the invention (shown with aside wall removed);

FIG. 6 is a schematic side view of a system for heat-treating aworkpiece according to a fourth embodiment of the invention (shown witha side wall removed);

FIG. 6A is a cross-sectional view in side elevation of a heating deviceand a filtering device of the heat-treating system shown in FIG. 6;

FIG. 7 is a schematic side view of a system for heat-treating aworkpiece according to a fifth embodiment of the invention (shown with aside wall removed);

FIG. 7A is a cross-sectional view in side elevation of a heating deviceand a filtering device of the heat-treating system shown in FIG. 7; and

FIG. 8 is a schematic side view of a system for heat-treating aworkpiece according to a sixth embodiment of the invention (shown with aside wall removed).

DETAILED DESCRIPTION

Referring to FIG. 1, a system for heat-treating a workpiece according toa first embodiment of the invention is shown generally at 20. The systemincludes a pre-heating device 22 operable to pre-heat the workpiece 24to an intermediate temperature, and a heating device 26 operable to heata surface 28 of the workpiece to a desired temperature greater than theintermediate temperature. The system further includes a coolingenhancement system 29 for enhancing cooling of the workpiece to atemperature below the intermediate temperature.

System

Referring to FIG. 2, a system for heat-treating a workpiece according toa second embodiment of the invention is shown generally at 30. Thesystem 30 includes a pre-heating device 32, operable to pre-heat aworkpiece 34, which in this embodiment is a semiconductor wafer, to anintermediate temperature. The system further includes a heating device36, which in this embodiment is operable to heat a surface 38 of theworkpiece 34 to desired temperature greater than the intermediatetemperature.

In this embodiment, the pre-heating device 32 is operable to pre-heatthe workpiece 34 from an initial temperature to the intermediatetemperature, and the heating device 36 is operable to heat the surface38 of the workpiece 34 to the desired temperature, which is greater thanthe intermediate temperature by an amount less than or equal to aboutthe difference between the intermediate and initial temperatures. Inother words, a significant portion of the heating occurs during theheating from the initial temperature to the intermediate temperature. Inthis embodiment, the heating device is operable to commence the heatingwithin less time following the first time period than the first timeperiod. More particularly, in this embodiment the heating device isoperable to commence the heating of the surface substantiallyimmediately when the workpiece reaches the intermediate temperature.

Also in this embodiment, the pre-heating device 32 includes a firstirradiance source 40 operable to irradiate a first side 42 of theworkpiece 34 to pre-heat the workpiece 34 to the intermediatetemperature. The heating device 36 includes a second irradiance source44 operable to irradiate a second side 46 of the workpiece 34, which inthis embodiment is co-extensive with the surface 38 of the workpiece 34,to heat the second side 46 to the desired temperature greater than theintermediate temperature. Note, however, that in an alternativeembodiment, the heating device 36 also may be activated while thepre-heating device 32 is activated for pre-heating the workpiece. Thus,if desired, the pre-heating may be achieved by using both the heatingdevice 36 and the pre-heating device 32.

As the workpiece 34 in the present embodiment is a semiconductor wafer,the heat-treating system 30 effectively acts as a semiconductor heatingapparatus.

Process Chamber

Still referring to FIG. 2, in this embodiment, the system 30 includes acooling enhancement system shown generally at 47 for enhancing coolingof the workpiece to a temperature below the intermediate temperature. Inthis embodiment, the cooling enhancement system 47 includes anabsorption system operable to absorb radiation thermally emitted by theworkpiece. More particularly, in this embodiment the absorption systemincludes a radiation absorbing environment operable to absorb radiationreflected and thermally emitted by the workpiece 34. More particularlystill, in this embodiment the radiation absorbing environment isprovided by a radiation absorbing chamber 48 surrounding the workpiece34. The radiation absorbing chamber 48 includes walls 50, 52, 54 and 56,each of which acts as a radiation absorbing surface operable to absorbthe radiation reflected and thermally emitted by the workpiece 34. Thus,in this embodiment, the absorption system of the cooling enhancementsystem 47 includes a radiation absorbing surface, which in turn includesa wall of a radiation absorbing chamber.

In this embodiment the walls 50, 52, 54 and 56 are made of blackstainless steel. Alternatively, other suitable radiation-absorbingmaterials may be used, such as anodized aluminum, for example. As afurther alternative, the walls may be composed of virtually anythermally conductive material and coated with a radiation-absorbingsubstance, such as paint containing graphite, for example.

In this embodiment, the absorption system of the cooling enhancementsystem 47 further includes a selective-filtering system, discussed ingreater detail below.

Generally, the radiation-absorbing effect of the cooling enhancementsystem 47, or more particularly of the radiation absorbing chamber 48,serves to increase the response time of the system 30, so that theworkpiece 34 begins to cool more quickly after the pre-heating andheating devices 32 and 36 are switched off than it would if a reflectivechamber were substituted for the radiation absorbing chamber 48. Thisincreased system response time results in a more sharply-definedtemperature profile in which the surface 38 of the workpiece 34 spendsless time at the highest temperatures involved in any given thermalcycle. Where the workpiece 34 is an ion-implanted semiconductor wafer,this tends to reduce the dopant diffusion depth during the thermalcycle, allowing for the formation of shallower junctions. In addition,using the radiation absorbing chamber 48 reduces possible damage to thecrystal lattice of such a workpiece, as compared to systems usingreflective chambers, which non-uniformly reflect radiation back to theworkpiece which then non-uniformly absorbs such radiation, giving riseto increased thermal gradients and thermal stress in the workpiece. Thecooling enhancement system 47 not only improves the uniformity of theheating of the workpiece by removing any such re-reflections during theheating stages, but additionally, during the cooling stages when theheating sources are deactivated, the cooling enhancement system enhancescooling of the workpiece by preventing radiation thermally emitted bythe workpiece from being reflected back to the workpiece, which wouldtend to re-heat the workpiece. Thus, the overall rate of cooling isenhanced by the effect of the absorption system of the coolingenhancement system 47, thereby further reducing dopant diffusion in theworkpiece. In this embodiment, the cooling enhancement system 47 allowsthe workpiece to cool at a rate of at least 100° C. per second, or moreparticularly, at a rate of at least 180° C. per second. Alternatively,however, a reflective chamber may be substituted for the radiationabsorbing chamber 48, if desired, which would increase the energyefficiency of the thermal cycle at the expense of greater dopantdiffusion and thermal stress in the workpiece.

In this embodiment, the system 30 further includes a cooling subsystem58 operable to cool the radiation absorbing surfaces of the walls 50,52, 54 and 56 of the radiation absorbing chamber 48. More particularly,in this embodiment the cooling subsystem 58 is a water circulationsystem, although alternatively other cooling enhancement systems may besubstituted. Alternatively, the cooling subsystem 58 may be omitted,although this would be undesirable if radiation absorbing surfaces aresuch as walls 50, 52, 54 and 56 are provided, as the radiation absorbingsurfaces would otherwise tend to become hot and thermally emitradiation, which would continue to heat the workpiece 34 after thepre-heating and heating devices 32 and 36 are deactivated, therebyslowing the response time of the system 30. For a similar reason, in thepresent embodiment, in which the cooling enhancement system 47 includesa selective-filtering system (discussed in greater detail further below)such as one or more water-cooled windows, the cooling subsystem 58 mayalso be used to cool the selective-filtering system. Similarly, thecooling subsystem 58 may be used to cool any other windows of the system30, such as a window 53 discussed below, for example.

In this embodiment the system 30 further includes a temperatureindicator 60 operable to produce an indication of a temperature of theworkpiece. More particularly, in this embodiment the temperatureindicator 60 includes a measuring system such as that disclosed incommonly-owned U.S. Pat. No. 6,303,411, issued Oct. 16, 2001, which isincorporated herein by reference. Thus, in the present embodiment thetemperature indicator 60 includes a charge-coupled device (CCD) mountedbeneath a quartz window 53 in the wall 52 of the radiation absorbingchamber 48, and further includes a CCD optics system (not shown) and aband-pass filter (not shown) interposed between the CCD and the window53, and a radiation sensor (not shown) mounted on a lower surface of aninternal wall 57 of the radiation absorbing chamber 48. Alternatively,other temperature indicators, such as a pyrometer for example, may besubstituted for the temperature indicator. As a further alternative, thetemperature of the workpiece 34 may simply be predicted from the powersupplied to the workpiece, without the necessity of directly measuringthe workpiece temperature.

The internal wall 57 in the radiation absorbing chamber 48 extendsbetween the walls 50 and 56 of the radiation absorbing chamber. Anannular guard ring 61 is set in a disc-shaped opening 59 in the internalwall 57 and extends radially inward into the opening 59. The guard ring61 includes the same or similar material as the workpiece, which in thisembodiment is a silicon semiconductor wafer. The guard ring is used toreduce edge effects during the thermal cycle, and acts as a locator forlocating the workpiece in a desired position relative to the pre-heatingand heating devices 32, 36. Alternatively, other means for supportingthe workpiece may be substituted.

In addition, if desired, the radiation absorbing chamber 48 may includegas flow ports (not shown) and flow controllers (not shown) forcontrolling gas flows in the vicinity of the workpiece, although suchelements are not necessary for typical annealing applications.

Workpiece

Still referring to FIG. 2, in this embodiment, the workpiece 34 is asemiconductor wafer. More particularly, in this embodiment thesemiconductor wafer is a silicon wafer used in the manufacture ofsemiconductor chips, such as microprocessors and memory devices, forexample. The first side 42 of the workpiece 34 is a substrate side,while the second side 46 is a device side. Thus, as shown in FIG. 2, inthis embodiment, the first and second irradiance sources 40 and 44 arelocatable to irradiate the substrate side and the device side,respectively, of a semiconductor wafer. The device side (the second side46) of the silicon wafer workpiece 34 has been previously subjected toan ion implantation process, such as ultra-low energy boron implantationfor the formation of shallow p+/n junctions, for example, to implantimpurity or dopant atoms into surface regions of the device side. As aresult of such ion implantation, the workpiece suffers crystallinelattice damage, and the boron implants tend to remain concentratedlargely at interstitial locations where they are electrically inactive,in a high boron concentration layer produced by the implant in thevicinity of the second side 46. Therefore, the workpiece 34 must besubjected to an annealing process to force the implants intosubstitutional sites in the lattice of the silicon wafer, therebyrendering them electrically active, and to repair the crystallinelattice damage suffered during ion implantation.

Alternatively, however, embodiments of the present invention haveapplications beyond mere activation of implanted dopants and thereforethe workpiece 34 may alternatively include a wafer that is to beannealed for different purposes. For example, other embodiments of theheat-treating methods and systems exemplified herein may be applied toanneal layers of metals, oxides, nitrides, silicides, silicates ortransition metal oxides on regions of the wafer. Similarly, otherembodiments may also be used to thermally oxidize or to thermallynitridize regions of the wafer, or to drive chemical vapor deposition oflayers on the wafer, or to drive solid state reactions within the bulkand the near surface regions of the wafer, to name but a few examples.

More generally, it is expected that many types of workpieces thatinclude a base material coated with a plurality of layers of differingmaterials may benefit from embodiments of the heat-treating methodsexemplified herein. In this regard, the base material may include asemiconductor such as silicon, silicon carbide or gallium arsenide, forexample, but alternatively, may include a magnetic medium used tofabricate memory media or magnetic read/write heads, or may include aglass used to fabricate flat panel displays, for example. Suchworkpieces may or may not have been subjected to a surface modificationprocess such as pre-amorphization, and the layers may be eitherlaterally continuous or discontinuous (as a result of intentionalpatterning) across the surfaces of the base material, or a combinationof continuous and discontinuous layers.

More broadly, however, the workpiece 34 need not be any of the abovetypes of workpieces, but may alternatively include any other type ofworkpiece that would benefit from the heat-treating methods and systemsdisclosed herein.

Pre-Heating Device

Still referring to FIG. 2, in this embodiment, the pre-heating device32, or more particularly the first irradiance source 40, includes an arclamp 62 operable to irradiate the workpiece 34 with electromagneticradiation. More particularly, in this embodiment the arc lamp 62 is a500 kW double water wall argon plasma arc lamp available from VortekIndustries Ltd. of Vancouver, British Columbia, Canada. An example ofsuch an arc lamp is disclosed in commonly-owned Patent CooperationTreaty application Ser. No. PCT/CA01/00051, published Jul. 26, 2001under Publication No. WO 01/54166, which is hereby incorporated hereinby reference. Such arc lamps provide numerous advantages forsemiconductor annealing as compared to tungsten filament lamp sources.For example, as a result of the low thermal mass of argon plasmas, theresponse time of the arc lamp 62 is on the order of 0.1 or 0.2 ms orless, which is not only faster than a thermal conduction time for asilicon wafer but is also three orders of magnitude faster than responsetimes of typical tungsten filament lamps. The arc lamp 62 thus permits afaster thermal cycle resulting in less dopant diffusion than tungstenfilament annealing systems. In addition, the arc lamp 62 produces over95% of its spectral distribution below the 1.2 μm band gap absorption ofcold silicon, as compared to 40% for typical tungsten lamp sources,resulting in greater heating efficiency. Also, the plurality of tungstenfilament lamps in a typical tungsten annealing system are not perfectlycalibrated with one another and their irradiance spectra also changeover time due to changes in the filament, accumulation of deposits onlamp bulb surfaces, etc. Therefore, the use of the single arc lamp 62,whose irradiance does not appreciably change over time, increases theuniformity of irradiation of the workpiece, resulting in lower thermalgradients in the workpiece and less corresponding thermal damage to thelattice, and eliminates the need for frequent calibration andre-calibration of a large number of energy sources, such as an array oftungsten lamps, for example. Similarly, the long lifetime of the arclamp 62 eliminates the need for frequent replacement and re-calibrationof burned-out bulbs. Alternatively, however, other types of pre-heatingdevices, including even tungsten filament lamp sources or arrays of suchlamp sources, may be substituted.

In this embodiment the pre-heating device 32 further includes areflector 64. The reflector 64 is formed by a series of flat segmentsforming a trough shape, so as to cooperate with the arc lamp 62 toproduce a generally uniform irradiance field. In this embodiment, thereflector 64 includes a reflector manufactured by Vortek IndustriesLtd., of Vancouver, Canada. Alternatively, the reflector 64 may beomitted or replaced with other reflectors, although it is desirable thatthe irradiance field be generally uniform.

The arc lamp 62 is positioned at a focal point of the reflector 64, andthe arc lamp 62 and the reflector 64 are positioned to irradiate thefirst side 42 of the workpiece 34 with a substantially uniformirradiance field at an angle of incidence of 45 degrees relative to thesurface of the first side 42 of the workpiece.

In this embodiment, the radiation absorbing chamber 48 further includesa quartz window 65 extending between the walls 52 and 56 of theradiation absorbing chamber. The quartz window 65 serves to isolate thearc lamp 62 and reflector 64 from the interior of the radiationabsorbing chamber 48, to prevent contamination of the workpiece, lamp orreflector.

In the present embodiment, the pre-heating device 32 further includes acontinuous power supply (not shown) for supplying power to the arc lamp62 for continuous operation to pre-heat the workpiece. In this regard,the pre-heating device of the present embodiment is operable to pre-heatthe workpiece at a rate of at least 100° C. per second, up to anintermediate temperature in the range of from 600° C. to 1250° C. Moreparticularly, in this embodiment the ramp rate is at least 250° C. persecond, or more particularly still, the rate is at least 400° C. persecond. To achieve such ramp rates, the arc lamp 62 is capable ofirradiating the first side 42 of the workpiece with an intensity ofapproximately 1×10² W/cm² to achieve a ramp rate moderately in excess of250° C. per second, or an intensity of approximately 1.4×10² W/cm² toachieve a ramp rate moderately in excess of 400° C. per second, suchradiation intensities being determined by the input power supplied tothe arc lamp. Alternatively, the arc lamp is capable of accepting acontinuous range of input power levels and accordingly, faster or slowerramp rates may be substituted, although slower rates tend to result inincreased dopant diffusion, and much faster rates (on the order of thethermal lag time of the workpiece, for example) may result in largerthermal gradients in the workpiece. For example, ramp rates on the orderof 50° C. per second may well be adequate for some applications, whereasmuch faster ramp rates may be acceptable for other applications.

Additionally, in the present embodiment the system 30 includes acorrective energy source 66 mounted beneath a quartz window 67 in thewall 52 of the radiation absorbing chamber 48. The corrective energysource supplies additional heating to cooler regions of the workpiece 34during a thermal cycle, to increase the uniformity of the temperaturedistribution in the workpiece, thereby reducing lattice damage caused bythermal stresses. More particularly, in this embodiment the correctiveenergy source is similar to that disclosed in the above-notedcommonly-owned U.S. Pat. No. 6,303,411. Alternatively, however, thecorrective energy source 66 may be omitted entirely, or other types ofcorrective energy sources may be substituted.

Heating Device

Still referring to FIG. 2, in this embodiment the heating device 36, ormore particularly the second irradiance source 44, includes a source ofthermal flux energy, to rapidly heat the surface 38 to the desiredtemperature. More particularly, in this embodiment the heating device 36includes a flash lamp 68 operable to irradiate the workpiece 34, or moreparticularly the surface 38, with electromagnetic radiation. The flashlamp 68 includes a VORTEK(™) double water wall arc lamp similar to thatdisclosed in the above-noted commonly-owned Patent Cooperation Treatyapplication Ser. No. PCT/CA01/00051. The flash lamp 68 includes a powersupply system 69, which in this embodiment includes not only acontinuous power supply similar to that provided in the pre-heatingdevice 32 for operating the flash lamp in a continuous mode if desired,but also includes a pulsed discharge unit that may be pre-charged thenabruptly discharged in order to supply a “spike” of input power to theflash lamp 68. More particularly, in this embodiment the power supplysystem 69 of the flash lamp includes a power supply model number VT-20pulsed discharge unit manufactured by Rapp OptoElectronin of Hamburg,Germany, operable to produce pulses of up to 60 kJ within aone-millisecond discharge time. Alternatively, other types of powersupplies operable to supply abrupt spikes of input power may besubstituted. For example, a power supply model number PS5010manufactured by EKSMA Company of Vilnius, Lithuania may be suitable formany applications. Preferably, any such power supply has a switchingfrequency of at least 2 kHz, and a power output of at least 500 kW,however, these preferred characteristics are not essential and may bevaried if desired.

More generally, other types of flash lamps, or more broadly, otherheating devices, may be substituted. However, the VORTEK(™) double waterwall arc lamp is preferred, as it can produce much higher-poweredflashes than other types of heating devices. In this regard, the heatingdevice 36 preferably includes a minimal number of heat sources, mostpreferably a single source, in order to simplify control of the heatingdevice and to improve uniformity of the irradiance field, without theneed for ongoing calibration of a large number of sources. Use of an arclamp is favored because the arc lamp has significantly higher poweroutput capabilities as compared to other types of heat sources, such astungsten filament lamps, for example. Conventional arc lamps mayexperience difficulties in producing a flash at the power levelsdisclosed herein, due to severe thermal stresses imposed upon the quartzwindows surrounding the arc resulting not only from conduction of heatfrom the arc, but also from absorption within the quartz windows ofradiation from the arc. In conventional arc lamps, these resultingthermal stresses may cause the quartz window surrounding the arc toviolently shatter. The VORTEK (™) double water wall arc lamp addressesthese difficulties, and is therefore capable of safely producing muchhigher-power flashes than conventional arc lamps, making it ideallysuited for the application of the present embodiment where a single lampor limited number of lamps are used.

In response to a discharge of the power supply system 69, the flash lamp68 is operable to produce a flash of electromagnetic radiation with apower output of 4-6 MW ranging from 1-5 ms in duration. For example, a 6MW flash of 1 ms duration may be advantageous for some applications. Byproducing such a flash when the workpiece is at the intermediatetemperature, the heating device 36 is operable to heat the surface 38 ofthe workpiece from the intermediate temperature to the desiredtemperature. In embodiments where the workpiece 34 is a siliconsemiconductor wafer, the heating device is operable to heat the surface38 to a desired temperature which is usually in the range of 1050° C. to1430° C.

The flash lamp 68 is advantageous for the purposes of the presentembodiment, in comparison to other ultra-fast heating devices. Forexample, although excimer lasers have been previously used for someannealing purposes, the monochromatic radiation produced by a lasertends to give rise to optical interference effects produced by thinfilms which coat the surface of a semiconductor wafer workpiece andwhich are intentionally laterally inhomogeneous. Such opticalinterference effects produce lateral temperature gradients which resultin thermal stress damage to the lattice of the workpiece. The flash lamp68 is less susceptible to such interference effects than lasers, due tothe broader spectrum of the electromagnetic radiation produced by theflash lamp. In addition, laser annealing typically requires multipleheating cycles, such as hundreds of cycles for example, to anneal theentire workpiece surface, and accordingly, if a laser were substitutedas the heating device, the workpiece likely would spend a longer amountof time at the intermediate temperature, resulting in deeper dopantdiffusion. Also, use of a laser as the heating device tends to producelower quality junctions than the flash lamp, resulting in higher currentleakage. In addition, the faster ramp time associated with lasers(typically two orders of magnitude faster than that associated with theflash lamp) tends to produce higher thermal gradients, increasing thelikelihood of lattice damage. Finally, due to the extremely shallow heatpenetration resulting from laser annealing, it is sometimes not possibleto achieve proper annealing of a desired layer such as a thin gate thatlies underneath an intervening layer, due to “shadowing” by theintervening layer, whereas in contrast the flash lamp tends to heat theentire surface region, including the intervening and underlying layer,to sufficient annealing temperatures.

Alternatively, however, if desired, other types of heating devices maybe substituted for the flash lamp 68. For the purposes of the presentembodiment, it is desirable that any alternative heating device have aresponse time faster than the thermal conduction time of the workpiece34 (typically on the order of 10-15 ms) and be capable of heating thesecond side 46 of the workpiece from the intermediate temperature to thedesired temperature in less time than the thermal conduction time of theworkpiece, so that the bulk of the workpiece 34 will remain atsubstantially the intermediate temperature in order for the bulk to actas a heat sink to facilitate rapid cooling of the second side 46 fromthe desired temperature to the intermediate temperature.

In this embodiment, the heating device 36 further includes a reflector70. In this embodiment the reflector 70 is formed by a series of flatsegments forming a trough shape, so as to cooperate with the flash lamp68 to produce a generally uniform irradiance field. In this embodiment,the reflector 70 includes a reflector manufactured by Vortek IndustriesLtd., of Vancouver, Canada. Alternatively, the reflector 70 may beomitted or replaced with other reflectors, although it is desirable thatthe irradiance field be generally uniform.

The flash lamp 68 is positioned at a focal point of the reflector 70,and the flash lamp and the reflector are positioned to irradiate thesecond side 46 of the workpiece 34 with a substantially uniformirradiance field at an angle of incidence of 45 degrees relative to thesurface of the second side 46 of the workpiece 34.

In this embodiment, the radiation absorbing chamber 48 further includesa quartz window 71 extending between the walls 50 and 54 of theradiation absorbing chamber. The quartz window 71 serves to isolate theflash lamp 68 and the reflector 70 from the interior of the radiationabsorbing chamber 48, to prevent contamination of the workpiece.

Selective-filtering System

Referring to FIG. 2, in this embodiment the absorption system of thecooling enhancement system 47 includes a selective-filtering system.More particularly, the selective-filtering system includes a firstfiltering device, which in this embodiment includes the quartz window65. The first filtering device, or more particularly, the quartz window65, is interposed between the pre-heating device 32 and the workpiece34, and is configured to transmit radiation produced by the pre-heatingdevice to the workpiece, to pre-heat the workpiece to the intermediatetemperature. More particularly still, the first filtering device isconfigured to transmit the radiation to a surface of the workpiece,which in this embodiment includes the substrate side, referred to hereinas the first side 42. The first filtering device is further configuredto absorb radiation thermally emitted by the workpiece.

Similarly, in this embodiment the selective-filtering system furtherincludes a second filtering device, which in this embodiment includesthe quartz window 71. The second filtering device, or more particularly,the quartz window 71, is interposed between the heating device 36 andthe workpiece 34 and is configured to transmit radiation produced by theheating device to the surface 38 of the workpiece, to heat the surfaceto the desired temperature greater than the intermediate temperature.The second filtering device is further configured to absorb radiationthermally emitted by the workpiece.

Referring to FIGS. 2 and 2A, in this embodiment the second filteringdevice of the selective-filtering system of the cooling enhancementsystem 47 includes at least one window, which in this embodiment is thequartz window 71. More particularly, in this embodiment the quartzwindow 71 includes first and second spaced apart windows 82 and 84,which in this embodiment are constructed of quartz. In this embodimentthe windows 82 and 84 are optically transparent, and define a fluidchannel 86 interposed therebetween. The optically transparent windowspreferably have a thickness in the range of 2 to 10 mm and are spacedapart approximately 2 to 5 mm, preferably about 3 mm.

In this embodiment, the heat-treating system 30 further includes thecooling subsystem 58 for cooling the selective-filtering system, or moreparticularly, for cooling the first and second filtering devicesthereof. To achieve this, in the present embodiment the coolingsubsystem 58 includes a liquid-cooling subsystem for causing a liquid toflow across a surface of the window 71. More particularly still, in thisembodiment the liquid-cooling subsystem causes a liquid to flow in aspace, namely the fluid channel 86, defined between the windows 82 and84. Thus, in this embodiment, a cooling fluid, preferably a liquid suchas water, more preferably purified water and most preferably deionizedwater is pumped through the fluid channel 86. The cooled window 71having water pumped through fluid channel 86 readily transmits visibleand near-visible radiation (represented by wave lines 85) havingwavelengths from about 0.2 to 1.4 μm from the flash lamp 68 to theworkpiece, yet also absorbs infrared radiation of wavelengths greaterthan 1.4 μm emitted from the workpiece (represented by wave lines 88).By absorbing longer wavelength radiation emitted radiantly by theworkpiece, the cooled window 71 actively promotes workpiece cooling andreduces or eliminates reflections of workpiece-emitted radiation back tothe workpiece. This system 30 provides greater control and maximizescooling of the workpiece. After absorbing radiation, the water is pumpedaway from the window to further enhance cooling, as such pumpingprevents the cooled window 71 and the water therein from heating up andbeginning to thermally emit radiation. Radiation absorbed by the waterdoes not return to the workpiece where it would be reabsorbed. Incontrast, conventional highly reflective systems (not radiationabsorbing chambers) return most such radiation emitted by the wafer backto the wafer.

Thus, in this embodiment the cooled window 71 includes a first opticallytransparent plate (the window 82) cooled by a cooling fluid, and furtherincludes a second optically transparent plate (the window 84) separatedfrom the first optically transparent plate to define a passageway (thefluid channel 86) through which the cooling fluid may flow.

In this embodiment, the quartz window 65 shown in FIG. 2 interposedbetween the pre-heating device 32 and the workpiece 34 is structurallysimilar to the quartz window 71. Therefore, in this embodiment thewindow 65 is also liquid-cooled, or more particularly, is a water-cooledquartz window.

Thus, in the present embodiment, in which the workpiece 34 is asemiconductor wafer, the system 30 effectively acts as a semiconductorheating apparatus, including a first heating source (one of thepre-heating device 32 and the heating device 36) for heating a firstsurface of a semiconductor wafer, a second heating source (the other oneof the pre-heating device 32 and the heating device 36) for heating asecond surface of the semiconductor wafer, and a first cooled window(one of the windows 65 and 71) disposed between the first heating sourceand the semiconductor wafer. The apparatus of the present embodimentfurther includes a second cooled window (the other one of the windows 65and 71) disposed between the second heating source and the semiconductorwafer. The first and second cooled windows absorb radiation thermallyemitted by the semiconductor wafer, to controllably cool thesemiconductor wafer at a rate of at least 100° C. per second.

Control Device

Referring to FIG. 2, in this embodiment the system 30 further includes aprocessor circuit 72, which in the present embodiment is housed within ageneral purpose computer 74. The processor circuit 72 is incommunication with the pre-heating device 32 and the heating device 36.In addition, in embodiments such as the present embodiment in which thetemperature indicator 60 and the corrective energy source 66 areprovided, the processor circuit is in further communication with suchdevices.

In this embodiment (FIG. 2), the computer 74 further includes a storagedevice 76 in communication with the processor circuit 72. Moreparticularly, the storage device 76 includes a hard disk drive and arandom access memory. The computer 74 further includes an input device78, which in this embodiment is a keyboard, and an output device 80,which in this embodiment is a color monitor. Alternatively, however,other storage, input and output devices may be substituted. Or, as afurther alternative, the processor circuit may be omitted entirely andreplaced with any other suitable means for controlling the pre-heatingand heating devices 32 and 36 in accordance with the methods exemplifiedherein.

Operation

Referring to FIGS. 2, 3 and 4, in this embodiment the storage device 76shown in FIG. 2 stores blocks of codes for directing the processorcircuit 72 to execute a heat-treating routine shown generally at 90 inFIG. 3. The heat-treating routine is executed by the processor circuitin response to user input received at the user input device 78indicating that a heat-treating cycle is to commence.

Generally, in this embodiment, the heat-treating routine 90 configuresthe processor circuit 72 to control the pre-heating device 32 and theheating device 36 to pre-heat the workpiece 34 to an intermediatetemperature, and to heat the surface 38 of the workpiece 34 to a desiredtemperature greater than the intermediate temperature. In thisembodiment, the heating commences within less time following the firsttime period than the first time period. More particularly, in thisembodiment the heating commences substantially immediately when theworkpiece reaches the intermediate temperature. Also in this embodiment,the desired temperature is greater than the intermediate temperature byan amount less than or equal to about one-fifth of a difference betweenthe intermediate temperature and an initial temperature of theworkpiece.

Generally, throughout the execution of the heat-treating routine 90, thewalls 50, 52, 54 and 56 of the radiation absorbing chamber 48 absorbradiation reflected and thermally emitted by the workpiece 34, and thequartz windows 65 and 71 similarly absorb radiation thermally emitted bythe workpiece, thus enhancing cooling of the workpiece. The coolingsubsystem 58 cools these walls and windows to prevent them from becominghot in response to such absorption and re-emitting such absorbed energyas blackbody radiation. Alternatively, however, such absorption andcooling may be omitted at the expense of temperature uniformity in theworkpiece during the execution of the heat-treating routine, and at thefurther expense of deeper dopant diffusion resulting from slower coolingrates.

The heat-treating routine 90 begins with a first block 100 of codesshown in FIG. 3, which directs the processor circuit 72 to pre-heat theworkpiece 34 to an intermediate temperature. To achieve this, block 100directs the processor circuit to activate the pre-heating device 32, ormore particularly the first irradiance source 40, to irradiate the firstside 42 of the workpiece 34 to pre-heat the workpiece to theintermediate temperature. More particularly, block 100 directs theprocessor circuit to control the arc lamp 62 shown in FIG. 2 tocontinuously irradiate the first side 42 of the workpiece with aconstant radiation intensity of approximately 1.4×10² W/cm², which ithas been found is sufficient to pre-heat the workpiece at a ramp ratemoderately in excess of 400° C. per second. Thus, in this embodimentirradiating the workpiece involves exposing the workpiece toelectromagnetic radiation produced by an arc lamp.

Block 100 also directs the processor circuit 72 to initialize theheating device 36, which in this embodiment is achieved by charging thepower supply system 69 of the flash lamp 68 shown in FIG. 2.

In addition, in embodiments in which the corrective energy source 66shown in FIG. 2 is to be used, block 100 further directs the processorcircuit 72 to control the corrective energy source 66 to produce adesired spatial temperature distribution across the workpiece during thepre-heating stage, as described in greater detail in the above-notedcommonly-owned U.S. Pat. No. 6,303,411. Alternatively, the correctiveenergy source 66 may be omitted.

Block 110 then directs the processor circuit 72 to determine whether theintermediate temperature has been achieved in the workpiece. In thisembodiment, block 110 directs the processor circuit to achieve this bymonitoring signals received from the temperature indicator 60 shown inFIG. 2 indicative of the temperature of the workpiece 34. Alternatively,however, block 110 may direct the processor circuit to act as atemperature indicator, to produce an indication of a temperature of theworkpiece based on the time elapsed since the pre-heating device wasactivated at block 100, in view of a predicted heating ratecorresponding to the intensity of radiation incident upon the workpiece,to determine whether the intermediate temperature has been achieved.Although the magnitude of the intermediate temperature will vary fromapplication to application, in the present embodiment the intermediatetemperature is 1000° C. and therefore, this temperature will be achievedin the workpiece after approximately 2.5 seconds of irradiation of theworkpiece by the pre-heating device 32. In effect, therefore, blocks 100and 110 direct the processor circuit to control the pre-heating device32 to pre-heat the workpiece for a time period greater than a thermalconduction time of the workpiece (which is on the order of 10-15 ms).

Upon determining at block 110 that the intermediate temperature has beenachieved in the workpiece 34, block 120 directs the processor circuit 72to heat the surface 38 of the workpiece 34 to a desired temperature thatis greater than the intermediate temperature. In this embodiment, thedesired temperature exceeds the intermediate temperature by an amountless than or equal to about one-fifth (or more particularly, less thanor equal to about one-twentieth) of a difference between theintermediate temperature and the initial temperature of the workpiece.As stated, in this embodiment, preferred intermediate temperatures arein the range of about 600° C. to 1250° C., and preferred desiredtemperatures are in the range of about 1050° C. to about 1430° C. (whichvery roughly corresponds to a melting point of silicon). In thisembodiment, this heating stage commences within less time following thefirst time period (during which the workpiece temperature was increasingto the intermediate temperature) than the first time period. Moreparticularly, as a result of the execution of block 110 and 120, theheating device 36 is operable to commence the heating of the surface 38of the workpiece in response to the indication from the temperatureindicator 60 that the temperature of the workpiece 34 is at least theintermediate temperature, or alternatively, where the temperatureindicator is omitted for example, the heating device is operable tocommence such heating at an end of the first time period (during whichthe temperature of the workpiece was increasing to the intermediatetemperature).

In other words, in this embodiment the heating device 36 is operable tocommence heating the surface 38 substantially immediately when theworkpiece 34 reaches the intermediate temperature. In this regard, inthe present embodiment the heating device is operable to commence theheating of the surface within less than one second after the workpiecereaches the intermediate temperature. More particularly, the heatingdevice is operable to commence the heating of the surface within lessthan one-quarter second after the intermediate temperature is reached.More particularly still, in this embodiment the heating device isoperable to commence such heating within less than 100 milliseconds, ormore particularly within 10 milliseconds, after the workpiece reachesthe intermediate temperature. Effectively, therefore, as the thermalconduction time through the workpiece is on the order of 10-15 ms, inthis embodiment the heating device is operable to commence the heatingof the surface within an interval following the arrival of the workpieceat the intermediate temperature, the interval having a duration lessthan or equal to a thermal conduction time of the workpiece. In thisregard, for some applications it may be desirable to delay commencementof the heating stage until slightly after the deactivation of thepre-heating device, to allow for the thermal lag of the workpiece (onthe order of 10-15 ms). However, any delay longer than this 10-15 msworkpiece conduction time in commencing this heating stage will tend toincrease dopant diffusion in the workpiece. Therefore, in general it ispreferable not to delay the commencement of the heating stage at all,but if a delay is desired for a particular application, it is typicallyundesirable to “hold” the workpiece temperature at the intermediatetemperature for longer than the time taken to heat the workpiece fromits initial temperature to the intermediate temperature.

To commence the heating stage in the present embodiment, block 120directs the processor circuit 72 to deactivate the pre-heating device 32(including the corrective energy source 66 if a corrective energy sourceis provided), and to activate the heating device 36 to heat the surface38 of the workpiece to the desired temperature. More particularly, inthis embodiment, block 120 directs the processor circuit 72 to commencethe heating stage by controlling the second irradiance source 44 toirradiate the second side 46 of the workpiece 34 to heat the second sideto the desired temperature, which is greater than the intermediatetemperature. The processor circuit is directed to achieve this bysignaling the flash lamp 68 shown in FIG. 2, to cause the flash lamppower supply system 69 to be discharged to produce a short-duration,high energy arc in the flash lamp, which irradiates the surface 38 ofthe workpiece at a power of approximately 5 MW, for a duration on theorder of 1 ms. Thus, in this embodiment irradiating the surface 38involves exposing the surface to electromagnetic radiation produced by aflash lamp.

This flash heats the surface 38 of the workpiece to the desiredtemperature, which in this embodiment is 1050° C. At this hightemperature and corresponding high kinetic energies, the dopant atomsimplanted in the surface 38 of the workpiece tend to eject silicon atomsfrom the lattice and occupy substitutional lattice sites formerlyoccupied by silicon atoms. The dopants thereby become electricallyactivated. The displaced silicon atoms tend to migrate towardinterstitial sinks such as the surface 38 of the workpiece, where theytend to be consumed by other processes such as oxidation.

The heat-treating routine 90 is then ended.

Referring to FIG. 4, a temperature-time profile of the surface 38 of theworkpiece 34 resulting from the foregoing execution of the heat-treatingroutine 90 is shown generally at 130. The temperature-time profile 130has four distinct stages, namely, a bulk pre-heating stage 132, asurface heating stage 134, a surface cooling stage 136 and a bulkcooling stage 138.

Referring to FIGS. 2, 3 and 4, the bulk pre-heating stage 132 resultsfrom the execution by the processor circuit 72 of blocks 100 and 110,and serves to pre-heat the workpiece 34 by increasing its temperatureover a first time period 133 from its initial temperature to theintermediate temperature. More particularly, in this embodiment, thepre-heating device 32 increases the temperature of the entire workpiece34 from its initial temperature (room temperature) to an intermediatetemperature of 1000° C. at a ramp rate of approximately 400° C. persecond. Pre-heating the workpiece in this manner to the intermediatetemperature, and in particular to an intermediate temperature that isrelatively close to the desired temperature, serves to reduce themagnitude of the temperature gradients that occur in the workpieceduring the subsequent surface heating stage 134 and therefore serves toreduce thermal stress damage to the lattice of the workpiece, incomparison to techniques such as laser annealing or microwave annealing.However, the relatively fast ramp rate of the bulk pre-heating stage 132and the correspondingly short time period spent by the workpiece at hightemperatures results in much less dopant diffusion in the workpiece thanother cycles that use slower ramp rates or that hold the workpiece at anintermediate temperature before the subsequent heating stage. In otherwords, in this embodiment, the duration of the bulk pre-heating stage132, while longer than the thermal conduction time of the workpiece, isshort compared to a characteristic time required for unacceptablediffusion to occur at the temperatures obtained during the bulkpre-heating stage.

The surface heating stage 134 results from the flash produced by theheating device 36 at block 120, and serves to heat the surface 38 of theworkpiece from the intermediate temperature to the desired temperature.As shown in FIG. 4, such heating of the surface commences within lesstime following the first time period 133 than the first time period 133.More particularly, in this embodiment the heating commencessubstantially immediately following the end of the first time period133, as soon as the intermediate temperature is achieved in theworkpiece 34. In this embodiment the flash increases the temperature ofthe surface 38 from the intermediate temperature of 1000° C. to thedesired annealing temperature of 1050° C. in approximately onemillisecond. Due to the short duration of the flash (on the order of 1ms), the heating device 36 is operable to heat the surface 38 of theworkpiece for a time period less than a thermal conduction time of theworkpiece (on the order of 10-15 ms). Therefore, the heating device 36heats the surface 38 of the workpiece much faster than such heat canconduct away from the surface 38 and into the workpiece, and as aresult, the bulk of the workpiece remains substantially at theintermediate temperature while the surface 38 is heated to the desiredtemperature.

Thus, during the surface cooling stage 136 that immediately follows theflash, the relatively cold bulk of the workpiece 34 acts as a heat sinkfor the surface 38, allowing the surface 38 to cool at a significantlyfaster rate than it would have cooled if the entire workpiece had beenheated to the desired temperature. This rapid cooling continues untilthe surface 38 has reached the same temperature as the remainder of theworkpiece 34 (approximately the intermediate temperature). Typically,the duration of this surface cooling stage 136 is on the order of theduration of the surface heating stage 134. As an illustrative example, asurface of a silicon semiconductor wafer may cool at a rate of 10,000°C. per second for example, depending on the (intermediate) temperatureof the bulk of the wafer.

As a result of this ultra-fast heating and cooling during the surfaceheating and cooling stages 134 and 136, the surface 38 of the workpiecespends considerably less time in the high temperature range between theintermediate temperature and the desired temperature than it would haveif the entire workpiece had been heated to the desired temperature. Asmost of the undesirable dopant diffusion occurs at or near the desiredannealing temperature, this ultra-fast heating and cooling results inless dopant diffusion, allowing for the formation of shallower p+/njunctions than previous arc lamp or filament lamp annealing systems. Atthe same time, because the desired temperature exceeds the intermediatetemperature by an amount less than or equal to about one-fifth (or moreadvantageously in the present embodiment, less than or equal to aboutone-twentieth) of the difference between the intermediate and initialtemperatures, the temperature gradients in the workpiece during theseheating and cooling stages are much smaller than those that occur inconventional laser annealing techniques, resulting in less thermalstress damage to the crystal lattice.

When the surface 38 has cooled to the same temperature as the bulk ofthe workpiece 34 (approximately the intermediate temperature), the bulkcooling stage 138 then commences, in which the surface 38 cools alongwith the bulk of the workpiece 34. In this embodiment, such coolingresults largely from blackbody radiation thermally emitted by the hotworkpiece, but also results partly from convection involving gases (ifany) in the vicinity of the workpiece. The rate of such bulk cooling isstrongly dependent on temperature and also depends on other factors suchas the absorptiveness or reflectivity of the chamber, for example. Inthis embodiment the bulk cooling stage initially commences at a ramprate of approximately −180° C./s, although this rate decreases somewhatas the workpiece cools. Advantageously, the radiation absorbingproperties of the cooling enhancement system 47 and radiation absorbingchamber 48 allow faster bulk cooling rates than conventional reflectivechambers.

As discussed above in connection with FIG. 2A, additional means tocontrollably cool the workpiece 34 from the intermediate temperature areprovided. While the thermal flux heating ceases upon de-activation ofthe flash lamp 68, and cooling of the second side 46 from the desiredtemperature to the intermediate temperature occurs rapidly during thesurface cooling stage 136 as discussed above, cooling from theintermediate temperature to room temperature (or to a temperature belowthe intermediate temperature at which the workpiece is removed from thesystem) does not proceed rapidly without assistance. Thermal exposuremay be undesirably large if the workpiece remains at or close to theintermediate temperature for prolonged periods (e.g. 0.3 seconds orlonger). The water-cooled walls 50, 52, 54 and 56 of the radiationabsorbing chamber 48 and the cooled windows 71 and 65 associated withthe heating device 36 and the pre-heating device 32, absorb radiationemitted from the workpiece at wavelengths of 1.4 μm and above. For theexample of a silicon semiconductor wafer, this represents on the orderof 95% of the radiation emitted from the workpiece. In combination, theradiation absorbing chamber 48 and cooled windows 71 and 65 thuscontrollably cool the workpiece by removing from the radiation absorbingchamber 48 radiation emitted by the workpiece, preventing re-reflectionsof the radiation onto the workpiece. An example of such controlledcooling is illustrated by the bulk cooling stage 138 slope of the graphof FIG. 4.

Although only a single heat-treating routine 90 was described above forillustrative purposes, alternatively a plurality of differentheat-treating routines may be stored in the storage device 76 fordirecting the processor circuit 72 to control the system 30 to execute aplurality of different corresponding thermal heat-treating cycles fordifferent applications. For example, the workpiece 34 may be pre-heatedfor different times and/or at different rates to different intermediatetemperatures, and the second side 46 of the workpiece may then be heatedwith different power levels for different durations to different desiredtemperatures, depending upon the particular application.

Further Alternatives

If desired, pre-heating devices and heating devices other than the arclamp and flash lamp may be substituted.

For example, referring to FIGS. 2 and 5, a system for heat-treating aworkpiece according to a third embodiment of the invention is showngenerally at 200 in FIG. 5. In this embodiment, the pre-heating device32 includes an alternative irradiance source, which in this embodimentincludes at least one filament lamp. Thus, in this embodiment,irradiating the workpiece includes exposing the workpiece toelectromagnetic radiation produced by at least one filament lamp. Moreparticularly, in this embodiment the pre-heating device 32 includes adisc-shaped array 202 of tungsten filament lamps operable to projectelectromagnetic radiation through a quartz window 204 to irradiate thefirst side 42 of the workpiece 34, to pre-heat the workpiece to theintermediate temperature. Although there are numerous advantages tousing an arc lamp rather than a tungsten filament lamp array as thepre-heating device 32, as discussed earlier herein, the deeper dopantdiffusion that tends to result from tungsten filament lamps may notnecessarily be fatal for all applications, depending on the performancerequirements in a particular application.

As a further example, still referring to FIGS. 2 and 5, in thealternative system 200 shown in FIG. 5, the heating device 36 includes asource of adiabatic energy, to rapidly heat the surface 38 to thedesired temperature. More particularly, in this embodiment the heatingdevice includes a laser 206, such as an excimer laser or other suitablelaser, operable to irradiate the surface 38 by moving a laser beam 208across the surface. The laser 206 is operable to produce a rapid laserpulse, on the order of microseconds or nanoseconds in duration, to heatthe surface 38 to the desired temperature. Although the laser 206 maysuffice for applications where the increased thermal stress damage tothe lattice of the workpiece is not critical, it is noted that ingeneral, the flash lamp 68 shown in FIG. 2 is preferred, for reasonsdiscussed earlier herein.

Referring to FIGS. 2, 6 and 6A, a system for heat-treating a workpieceaccording to a fourth embodiment of the invention is shown generally at160 in FIG. 6. In this embodiment, a single arc lamp 162 functions asboth the pre-heating device 32 and the heating device 36. The arc lamp162 is similar to the arc lamp 62 shown in FIG. 2 and includes areflector 164 for providing a substantially uniform irradiance field toirradiate the second side 46 of the workpiece, which in this embodimentis a device side of a silicon semiconductor wafer. However, the arc lamp162 further includes a power supply system 166 similar to the powersupply system 69 of the flash lamp 68 shown in FIG. 2. The power supplysystem 166 includes a pulsed discharge unit similar to that of the powersupply system 69, which is connected in parallel with a regularcontinuous power supply (not shown) of the arc lamp 162.

Thus, referring to FIGS. 2, 3, 4 and 6, the arc lamp 162 may be operatedin a manner similar to the arc lamp 62 shown in FIG. 2 during the bulkpre-heating stage 132 shown in FIG. 4, in accordance with the executionby the processor circuit 72 of a modified block 100 of the heat-treatingroutine 90. When the intermediate temperature is achieved in theworkpiece, a modified block 110 directs the processor circuit 72 todisconnect the regular continuous power supply to the arc lamp 162, andto discharge the power supply system 166 to provide an abrupt spike ofpower to the arc lamp 162, producing a flash of similar intensity andduration to that produced by the flash lamp 68 shown in FIG. 2. Althoughthe system 160 shown in FIG. 6 may be less expensive than the system 30shown in FIG. 2, the system 160 supplies 100% of the heating of theworkpiece to the second side 46, which in this embodiment is the deviceside, of the workpiece. As the device side is much more inhomogeneousthan the substrate side (the first side 42) of the workpiece,non-uniform absorption by devices on the device side may tend to producegreater lateral temperature gradients and corresponding thermal stressdamage to the lattice of the workpiece than those that would occur usingthe system 30. This difficulty may be alleviated somewhat by providingthe system 160 with an additional corrective energy source 168 locatableto supply additional heat to cooler areas of the device side, whoseoperation is similar to that of the corrective energy source 66 shown inFIG. 2.

Referring to FIGS. 6 and 6A, in this embodiment a cooled window 170extends between the chamber walls to isolate the arc lamp from theworkpiece, and includes spaced-apart optically transparent windows 172and 174, preferably constructed of quartz, having a fluid channel 176interposed therebetween. The optically transparent windows preferablyhave a thickness in the range of 3 to 10 mm and are spaced apartapproximately 2 to 5 mm, preferably 3 mm. A cooling fluid, preferably aliquid such as water, is pumped through the fluid channel 176. Thecooled window 170 having water pumped through fluid channel 176 readilytransmits visible radiation (represented by wave lines 175) from the arclamp 162 to the workpiece, yet also absorbs infrared radiation ofwavelengths greater than 1.4 μm emitted from the workpiece (representedby wave lines 178). By absorbing radiation in wavelengths emittedradiantly by the workpiece, the cooled window 170 actively promotesworkpiece cooling and limits or eliminates reflections ofworkpiece-emitted radiation back to the workpiece. This system 160provides greater control and maximizes cooling of the workpiece.Alternatively, however, the window 170 may be omitted or replaced withother suitable window types if desired.

Referring back to FIGS. 5 and 6, further variations in the nature,location and combinations of the pre-heating and heating devices 32 and36 are possible. For example, lasers other than excimer lasers may besubstituted for the flash lamp 68 to act as the heating device 36. Or,different types of tungsten filament lamp arrays, such as a lineartungsten lamp array, may be substituted for the arc lamp 62 to act asthe pre-heating device 32.

As a further alternative, referring to FIGS. 2, 7 and 7A, a system forheat-treating a workpiece according to a fifth embodiment of theinvention is shown generally at 220 in FIG. 7. In this embodiment thepre-heating device 32 includes a radiant hot body 222 locatable topre-heat the workpiece to the intermediate temperature. In thisembodiment the hot body 222 is quartz, heated to approximately theintermediate temperature. Alternatively, other materials, such assilicon carbide, silicon, refractory metal, graphite, or a combinationof such materials, for example, may be substituted. The hot body 222 islocated in the radiation absorbing chamber 48 below the workpiece 34, inclose proximity thereto, and is operable to pre-heat the workpiece byradiative heat transfer and also by convection and conduction through athin layer of gas between the hot body 222 and the workpiece 34.Following the bulk pre-heating and surface heating stages 132 and 134,the hot body may be effectively “shut off” by moving the workpiece awayfrom the hot body, or alternatively, by moving the hot body away fromthe workpiece. In this embodiment, this is achieved by a motorizedmechanism 224 that slides the workpiece 34 out of the radiationabsorbing chamber 48 following the surface heating stage.

Referring to FIGS. 7 and 7A, in this embodiment a cooled window 230extends between the chamber walls to isolate the heating device 36 fromthe chamber holding the workpiece. In this embodiment, the cooled window230 includes spaced-apart optically transparent windows 232 and 234,preferably constructed of quartz, having a fluid channel 236 interposedtherebetween. The optically transparent windows preferably have athickness in the range of 3 to 10 mm and are spaced apart approximately2 to 5 mm, preferably 3 mm. A cooling fluid, preferably a liquid such aswater, is pumped through the fluid channel 236. The cooled window 230having water pumped through fluid channel 236 readily transmits visibleradiation (represented by wave lines 235) from the lamp of the heatingdevice 36 to the workpiece, yet also absorbs infrared radiation ofwavelengths greater than 1.4 μm emitted from the workpiece (representedby wave lines 238). By absorbing radiation in wavelengths emittedradiantly by the workpiece, the cooled window 230 actively promotesworkpiece cooling and limits or eliminates reflections ofworkpiece-emitted radiation back to the workpiece. This system 220provides greater control and maximizes cooling of the workpiece.Alternatively, however, the window 230 may be omitted or replaced withother suitable window types if desired.

Also, if separate pre-heating and heating devices are provided, thepre-heating and heating devices need not be on opposite sides of theworkpiece: for example, if desired, the pre-heating device, such as alinear tungsten lamp array, and a heating device such as a laser may beboth located above the surface 38 of the workpiece, to irradiate thesecond or device side 46 of the workpiece (although, as noted, supplying100% of the pre-heating and heating energy to the device side tends toproduce greater temperature gradients and thermal stress damage).

Referring to FIG. 8, an apparatus for heating a workpiece according to asixth embodiment of the invention is shown generally at 300. In thisembodiment the workpiece is a semiconductor wafer, and the apparatus 300includes a chamber housing the semiconductor wafer, the chamber havingone or more walls with a radiation-reflecting surface. Moreparticularly, in this embodiment the chamber of the apparatus 300includes axially aligned reflective chambers 302 and 304 separated fromone another by a workpiece-holding chamber 306. Each reflective chamber302, 304 has four sidewalls with the internal sidewall surfaces coatedwith a reflective coating 308, 310 that reflects radiation in thewavelength ranges emitted from arc lamp sources and emitted from theworkpiece. The sidewalls are slightly inwardly tapered toward theworkpiece-holding chamber 306, with the angle of the taper from about 2to 6 degrees from perpendicular, preferably about 3 degrees fromperpendicular. Unlike the chamber walls 50, 52, 54 and 56 of theradiation absorbing chamber 48 in the prior embodiments (i.e., FIG. 2),the sidewalls of the chambers 302, 304 in this sixth embodiment arereflective and may not be water cooled.

Within the workpiece-holding chamber 306, the workpiece 320 is held byits outer edges on a support ring 322. Alternatively, the workpiececould be supported on pins, or by other suitable means. As shown in FIG.8, the workpiece 320 is a semiconductor wafer. The workpiece 320 isloaded into and unloaded from the workpiece-holding chamber 306 in adirection generally perpendicular to the axis of the chambers 302, 304as indicated by arrow 312. The workpiece-holding chamber is sealed fromthe chambers 302, 304 preferably by optically transparent windows 314,316, although such windows are not required. Process gases and/or inertgases may be introduced into the workpiece-holding chamber throughconduits (not shown). For semiconductor wafer annealing processes,usually gases such as argon, nitrogen, NH₃, N₂O and NO, and mixtures ofthese gases or mixtures of one or more of these gases with oxygen, areintroduced into the chamber 306. Annealing may also be carried out in avacuum.

Arc lamps 324, 326 and associated reflector assemblies 328, 330 areprovided at the top and bottom of the apparatus, adjacent to thereflective chambers 302 and 304, respectively. The reflector assembliesare formed by a series of flat segments forming a trough shape, so as tocooperate with each arc lamp to produce a generally uniform irradiancefield. Examples of such reflectors are manufactured by Vortek IndustriesLtd. of Vancouver, Canada. Each arc lamp 324, 326 is positioned at afocal point of its associated reflector 328, 330, respectively. Each arclamp 324, 326 and its associated reflector assembly 328, 330,respectively, are positioned to irradiate one side of the workpiece 320with a substantially uniform irradiance field. As shown in FIG. 8, theradiant energy from arc lamp 324 irradiates the top surface 318 of theworkpiece 320. The reflectors 328, 330 direct the radiant energy towardthe workpiece without substantial reflection of that radiation on thereflective sidewalls of the chambers 302, 304. Optically transparentwindows 332, 334 are provided to further isolate the arc lamps 324, 326from the chambers 302, 304. The arc lamps are cooled by fluid introducedthrough cooling channels 336, 338 in each bulb housing.

The arc lamps 324, 326 and associated reflector assemblies 328, 330 eachare separated from the adjacent chamber 302, 304 by cooled windows 340,342. Cooled windows 340, 342 each include two optically transparentplates 344, 346 and 354, 356 spaced apart from one another and havingone or more channels 348 and 358 defined in that space through which acooling fluid, such as a liquid, preferably water, flows. The coolingliquid flows into the passages as indicated by arrows 350 and exits fromthe passages as indicated by arrows 360. The plates preferably areformed from quartz and have a thickness in the range of 2 to 10 mm,separated from one another about 2 to 5 mm, preferably 3 mm.

The cooled windows 340, 342 serve competing purposes. First, theyreadily transmit visible and near-visible radiation emitted by the arclamps (generally at wavelengths in the range of 0.2 to 1.4 μm) to heatthe workpiece without substantial attenuation or diminishment of theefficiency of heating. Second, they actively remove longer wavelengthradiation emitted from the workpiece (generally at wavelengths of 1.4 μmand above) out of the chamber thus preventing reflected radiation fromreturning to the workpiece, which serves to controllably cool theworkpiece from the intermediate temperature to room temperature or atemperature below the intermediate temperature at which the workpiecemay be removed from the workpiece-holding chamber after processing.Prior heating methods in reflective cavities without cooled windowslacked means to controllably cool the workpiece and prevent excessivethermal exposure at the intermediate or higher temperatures. With thecooled windows 340, 342 of the embodiment shown in FIG. 8, theworkpiece, such as a silicon semiconductor wafer, is cooled at rates inthe range of 100° C. to 200° C. per second, preferably 180° C. persecond or more. This compares to cooling rates of about 90° C. persecond for reflective chambers without water cooled windows.

Other combinations or permutations of the above-noted pre-heating andheating devices or equivalent devices may be provided. For example, anarc lamp may be provided as the pre-heating device and a laser as theheating device, or a tungsten filament lamp array may be provided as thepre-heating device and a flash lamp as the heating device. These andother such variations may be apparent to one of ordinary skill in theart upon reviewing this specification, and are not considered to departfrom the scope of the invention as construed in accordance with theaccompanying claims.

More generally, while specific embodiments of the invention have beendescribed and illustrated, such embodiments should be consideredillustrative of the invention only and not as limiting the invention asconstrued in accordance with the accompanying claims.

1. A method of heat-treating a workpiece, the method comprising: a)pre-heating the workpiece to an intermediate temperature; b) heating anentire surface of the workpiece to a desired temperature greater thanthe intermediate temperature, within a time period less than a thermalconduction time of the workpiece; and c) enhancing cooling of theworkpiece.
 2. The method of claim 1 wherein enhancing comprisesabsorbing radiation thermally emitted by the workpiece.
 3. The method ofclaim 2 wherein absorbing comprises absorbing the radiation at aradiation absorbing surface.
 4. The method of claim 3 wherein absorbingcomprises absorbing the radiation at a wall of a radiation absorbingchamber.
 5. The method of claim 2 wherein absorbing comprises absorbingthe radiation thermally emitted by the workpiece at aselective-filtering system.
 6. The method of claim 5 wherein pre-heatingthe workpiece comprises transmitting radiation produced by an irradiancesource through a filtering device of the selective-filtering system tothe workpiece.
 7. The method of claim 6 wherein transmitting comprisestransmitting the radiation to a second surface of the workpiece.
 8. Themethod of claim 5 wherein heating the surface of the workpiece comprisestransmitting radiation produced by an irradiance source through afiltering device of the selective-filtering system to the surface of theworkpiece.
 9. The method of claim 5 further comprising cooling theselective-filtering system.
 10. The method of claim 9 wherein coolingthe selective-filtering system comprises causing a liquid to flow acrossa surface of a window of the selective-filtering system.
 11. The methodof claim 9 wherein cooling the selective-filtering system comprisescausing a liquid to flow in a space defined between first and secondspaced apart windows of the selective-filtering system.
 12. The methodof claim 1 wherein heating the surface comprises rapidly heating thesurface to the desired temperature by activating a source of thermalflux or adiabatic energy.
 13. The method of claim 12 further comprisingdeactivating the source of thermal flux or adiabatic energy.
 14. Themethod of claim 1, wherein pre-heating the workpiece to the intermediatetemperature comprises pre-heating the workpiece to a temperature in therange of 600° C. to 1250° C.
 15. The method of claim 1, wherein heatingthe surface of the workpiece to the desired temperature comprisesheating the surface to a temperature in the range of 1050° C. to 1430°C.
 16. The method of claim 1, wherein pre-heating comprises pre-heatingthe workpiece for a time period greater than a thermal conduction timeof the workpiece.
 17. The method of claim 1, wherein heating the surfaceof the workpiece comprises commencing said heating substantiallyimmediately when the workpiece reaches the intermediate temperature. 18.The method of claim 17 wherein commencing comprises commencing saidheating within an interval following the arrival of the workpiece at theintermediate temperature, the interval having a duration less than orequal to a thermal conduction time of the workpiece.
 19. The method ofclaim 1, wherein the workpiece is a semiconductor wafer.
 20. The methodof claim 1, wherein pre-heating comprises pre-heating the workpiece at arate of at least 100° C. per second.
 21. The method of claim 1, whereinpre-heating comprises irradiating the workpiece with electromagneticradiation produced by an arc lamp.
 22. The method of claim 1, whereinheating comprises irradiating the workpiece with electromagneticradiation produced by a flash lamp.
 23. The method of claim 1, whereinenhancing comprises allowing the workpiece to cool at a rate of at leastabout 100° C. per second.
 24. A system for heat-treating a workpiece,the system comprising: a) a pre-heating device operable to pre-heat theworkpiece to an intermediate temperature; b) a heating device operableto heat an entire surface of the workpiece to a desired temperaturegreater than the intermediate temperature, within a time period lessthan a thermal conduction time of the workpiece; and c) a coolingenhancement system for enhancing cooling of the workpiece to atemperature below the intermediate temperature.
 25. The system of claim24 wherein said cooling enhancement system comprises an absorptionsystem operable to absorb radiation thermally emitted by the workpiece.26. The system of claim 25 wherein said absorption system comprises aradiation absorbing surface.
 27. The system of claim 26 wherein saidradiation absorbing surface comprises a wall of a radiation absorbingchamber.
 28. The system of claim 25 wherein said absorption systemcomprises a selective-filtering system.
 29. The system of claim 28wherein said selective-filtering system comprises a filtering deviceinterposed between said pre-heating device and the workpiece andconfigured to transmit radiation produced by said pre-heating device tothe workpiece.
 30. The system of claim 29 wherein said filtering deviceis configured to transmit the radiation to a second surface of theworkpiece.
 31. The system of claim 28 wherein said selective-filteringsystem comprises a filtering device interposed between said heatingdevice and the workpiece and configured to transmit radiation producedby said heating device to the surface of the workpiece.
 32. The systemof claim 28 further comprising a cooling subsystem for cooling saidselective-filtering system.
 33. The system of claim 32 wherein saidselective-filtering system comprises at least one window, and whereinsaid cooling subsystem comprises a liquid-cooling subsystem for causinga liquid to flow across a surface of said window.
 34. The system ofclaim 32 wherein said selective-filtering system comprises first andsecond spaced apart windows, and wherein said cooling subsystemcomprises a liquid-cooling subsystem for causing a liquid to flow in aspace defined between said windows.
 35. The system of claim 24 whereinthe heating device comprises a source of thermal flux or adiabaticenergy operable to rapidly heat the surface to the desired temperature.36. The system of claim 24, wherein said pre-heating device is operableto pre-heat the workpiece to a temperature in the range of 600° C. to1250° C.
 37. The system of claim 24 wherein said heating device isoperable to heat the surface to a temperature in the range of 1050° C.to 1430° C.
 38. The system of claim 24, wherein said pre-heating deviceis operable to pre-heat the workpiece for a time period greater than athermal conduction time of the workpiece.
 39. The system of claim 24,wherein said heating device is operable to commence heating the surfacesubstantially immediately when the workpiece reaches the intermediatetemperature.
 40. The system of claim 39, wherein said heating device isoperable to commence heating the surface within an interval followingthe arrival of the workpiece at the intermediate temperature, theinterval having a duration less than or equal to a thermal conductiontime of the workpiece.
 41. The system of claim 24, wherein the workpieceis a semiconductor wafer.
 42. The system of claim 24, wherein saidpre-heating device is operable to pre-heat the workpiece at a rate of atleast 100° C. per second.
 43. The system of claim 24, wherein saidpre-heating device comprises an arc lamp operable to irradiate theworkpiece with electromagnetic radiation.
 44. The system of claim 24,wherein said heating device comprises a flash lamp operable to irradiatethe workpiece with electromagnetic radiation.
 45. The system of claim24, wherein said cooling enhancement system allows the workpiece to coolat a rate of at least about 100° C. per second.
 46. A system forheat-treating a workpiece, the system comprising: a) means forpre-heating the workpiece to an intermediate temperature; b) means forheating an entire surface of the workpiece to a desired temperaturegreater than the intermediate temperature, within a time period lessthan a thermal conduction time of the workpiece; and c) means forenhancing cooling of the workpiece.
 47. The system of claim 46 whereinsaid means for enhancing comprises means for absorbing radiationthermally emitted by the workpiece.
 48. A selective-filtering system foruse in heat-treating a workpiece, the system comprising: a) a firstfiltering device configured to transmit radiation from a pre-heatingdevice to the workpiece to pre-heat the workpiece to an intermediatetemperature, and configured to absorb radiation thermally emitted by theworkpiece; and b) a second filtering device configured to transmitradiation from a heating device to a surface of the workpiece to heatthe surface to a desired temperature greater than the intermediatetemperature, and configured to absorb radiation thermally emitted by theworkpiece.
 49. The system of claim 48 further comprising a coolingsubsystem for cooling said first and second filtering devices.
 50. Thesystem of claim 48 wherein at least one of said first and secondfiltering devices comprises a liquid-cooled window.
 51. The system ofclaim 50 wherein said liquid-cooled window comprises a water-cooledquartz window.
 52. A method of heat-treating a workpiece, the methodcomprising: a) pre-heating the workpiece to an intermediate temperature;and b) heating a surface of the workpiece to a desired temperaturegreater than the intermediate temperature, said heating commencingsubstantially immediately when the workpiece reaches the intermediatetemperature.
 53. The method of claim 52 wherein heating the surface ofthe workpiece comprises commencing said heating within less than onesecond after the workpiece reaches the intermediate temperature.
 54. Themethod of claim 52 wherein heating the surface of the workpiececomprises commencing said heating within less than one-quarter secondafter the workpiece reaches the intermediate temperature.
 55. The methodof claim 52 wherein heating the surface of the workpiece comprisescommencing said heating within less than 1×10² milliseconds after theworkpiece reaches the intermediate temperature.
 56. The method of claim52 wherein heating the surface of the workpiece comprises commencingsaid heating within less than 1×10¹ milliseconds after the workpiecereaches the intermediate temperature.
 57. The method of claim 52 whereinheating the surface of the workpiece comprises commencing said heatingwithin an interval following the arrival of the workpiece at theintermediate temperature, the interval having a duration less than orequal to a thermal conduction time of the workpiece.
 58. The method ofclaim 52 wherein the pre-heating comprises pre-heating the workpiece fora time period greater than a thermal conduction time of the workpiece.59. The method of claim 52 wherein heating comprises heating the surfacefor a time period less than a thermal conduction time of the workpiece.60. The method of claim 52 wherein heating comprises commencing saidheating in response to an indication that the temperature of theworkpiece is at least the intermediate temperature.
 61. The method ofclaim 52 further comprising producing the indication.
 62. The method ofclaim 52 wherein pre-heating comprises irradiating the workpiece. 63.The method of claim 62 wherein irradiating comprises exposing theworkpiece to electromagnetic radiation produced by an arc lamp.
 64. Themethod of claim 62 wherein irradiating comprises exposing the workpieceto electromagnetic radiation produced by at least one filament lamp. 65.The method of claim 52 wherein pre-heating comprises pre-heating theworkpiece at a rate of at least 100° C. per second.
 66. The method ofclaim 52 wherein pre-heating comprises pre-heating the workpiece at arate of at least 400° C. per second.
 67. The method of claim 52 whereinheating the surface of the workpiece comprises irradiating the surface.68. The method of claim 67 wherein irradiating comprises exposing thesurface to electromagnetic radiation produced by a flash lamp.
 69. Themethod of claim 67 wherein irradiating comprises moving a laser beamacross the surface.
 70. The method of claim 52 further comprisingabsorbing radiation reflected and thermally emitted by the workpiece.71. The method of claim 70 wherein absorbing comprises absorbing theradiation in a radiation absorbing environment.
 72. The method of claim70 wherein absorbing comprises absorbing the radiation in at least oneradiation absorbing surface.
 73. The method of claim 72 furthercomprising cooling the at least one radiation absorbing surface.
 74. Asystem for heat-treating a workpiece, the system comprising: a) apre-heating device operable to pre-heat the workpiece to an intermediatetemperature; and b) a heating device operable to heat a surface of theworkpiece to a desired temperature greater than the intermediatetemperature, and operable to commence the heating of the surfacesubstantially immediately when the workpiece reaches the intermediatetemperature.
 75. The system of claim 74 wherein said heating device isoperable to commence the heating of the surface within less than onesecond after the workpiece reaches the intermediate temperature.
 76. Thesystem of claim 74 wherein said heating device is operable to commencethe heating of the surface within less than one-quarter second after theworkpiece reaches the intermediate temperature.
 77. The system of claim74 wherein said heating device is operable to commence the heating ofthe surface within less than 1×10² milliseconds after the workpiecereaches the intermediate temperature.
 78. The system of claim 74 whereinsaid heating device is operable to commence the heating of the surfacewithin less than 1×10¹ milliseconds after the workpiece reaches theintermediate temperature.
 79. The system of claim 74 wherein saidheating device is operable to commence the heating of the surface withinan interval following the arrival of the workpiece at the intermediatetemperature, the interval having a duration less than or equal to athermal conduction time of the workpiece.
 80. The system of claim 74wherein said pre-heating device is operable to pre-heat the workpiecefor a time period greater than a thermal conduction time of theworkpiece.
 81. The system of claim 74 wherein said heating device isoperable to heat the surface for a time period less than a thermalconduction time of the workpiece.
 82. The system of claim 74 furthercomprising a temperature indicator operable to produce an indication ofa temperature of the workpiece.
 83. The system of claim 82 wherein saidheating device is operable to commence the heating in response to anindication from said temperature indicator that the temperature of theworkpiece is at least the intermediate temperature.
 84. The system ofclaim 74 wherein said pre-heating device comprises means for irradiatingthe workpiece.
 85. The system of claim 74 wherein said pre-heatingdevice comprises an irradiance source operable to irradiate theworkpiece.
 86. The system of claim 85 wherein said irradiance sourcecomprises an arc lamp.
 87. The system of claim 85 wherein saidirradiance source comprises at least one filament lamp.
 88. The systemof claim 74 wherein said pre-heating device comprises a hot bodylocatable to pre-heat the workpiece.
 89. The system of claim 74 whereinsaid pre-heating device is operable to pre-heat the workpiece at a rateof at least 100° C. per second.
 90. The system of claim 74 wherein saidpre-heating device is operable to pre-heat the workpiece at a rate of atleast 400° C. per second.
 91. The system of claim 74 wherein saidheating device comprises means for irradiating the surface.
 92. Thesystem of claim 74 wherein said heating device comprises an irradiancesource operable to irradiate the surface.
 93. The system of claim 92wherein said irradiance source comprises a flash lamp.
 94. The system ofclaim 91 wherein said irradiance source comprises a laser.
 95. Thesystem of claim 74 further comprising a radiation absorbing environmentoperable to absorb radiation reflected and thermally emitted by theworkpiece.
 96. The system of claim 74 further comprising at least oneradiation absorbing surface operable to absorb radiation reflected andthermally emitted by the workpiece.
 97. The system of claim 96 furthercomprising a cooling subsystem operable to cool said at least oneradiation absorbing surface.
 98. A system for heat-treating a workpiece,the system comprising: a) means for pre-heating the workpiece to anintermediate temperature; and b) means for heating a surface of theworkpiece to a desired temperature greater than the intermediatetemperature, comprising means for commencing the heating substantiallyimmediately when the workpiece reaches the intermediate temperature. 99.The system of claim 98 wherein said means for commencing comprises meansfor commencing the heating within less than one second after theworkpiece reaches the intermediate temperature.
 100. The system of claim98 wherein said means for commencing comprises means for commencing theheating within less than one-quarter second after the workpiece reachesthe intermediate temperature.
 101. The system of claim 98 wherein saidmeans for commencing comprises means for commencing the heating withinless than 1×10¹ milliseconds after the workpiece reaches theintermediate temperature.
 102. The system of claim 98 wherein said meansfor commencing comprises means for commencing the heating within aninterval following the arrival of the workpiece at the intermediatetemperature, the interval having a duration less than or equal to athermal conduction time of the workpiece.
 103. A semiconductor heatingapparatus, comprising: a first heating source for heating a firstsurface of a semiconductor wafer to heat the wafer to an intermediatetemperature; a second heating source for heating an entire secondsurface of the semiconductor wafer within a time period less than athermal conduction time of the wafer, to heat the second surface to adesired temperature greater than the intermediate temperature; and afirst cooled window disposed between the first heating source and thesemiconductor wafer.
 104. The semiconductor heating apparatus of claim103, wherein the first cooled window comprises a first opticallytransparent plate cooled by a cooling fluid.
 105. The semiconductorheating apparatus of claim 104, wherein the first cooled window furthercomprises a second optically transparent plate separated from the firstoptically transparent plate to define a passageway through which thecooling fluid may flow.
 106. The semiconductor heating apparatus ofclaim 104, wherein the cooling fluid is water.
 107. The semiconductorheating apparatus of claim 104, wherein the first optically transparentplate is formed from quartz.
 108. The semiconductor heating apparatus ofclaim 105, wherein the second optically transparent plate is formed fromquartz.
 109. The semiconductor heating apparatus of claim 103, furthercomprising a second cooled window disposed between the second heatingsource and the semiconductor wafer.
 110. The semiconductor heatingapparatus of claim 103, wherein the first cooled window absorbsradiation thermally emitted by the semiconductor wafer.
 111. Thesemiconductor heating apparatus of claim 110, wherein the first cooledwindow absorbs radiation to controllably cool the semiconductor wafer ata rate of at least 100° C. per second.
 112. The semiconductor heatingapparatus of claim 109, wherein the second cooled window absorbsradiation to controllably cool the semiconductor wafer at a rate of atleast 100° C. per second.
 113. The semiconductor heating apparatus ofclaim 103, wherein the first heating source includes an arc lamp. 114.The semiconductor heating apparatus of claim 103, wherein the secondheating source includes an arc lamp.
 115. The semiconductor heatingapparatus of claim 103, wherein the first heating source is a tungstenlamp or array of tungsten lamps.
 116. The semiconductor heatingapparatus of claim 103, further comprising a chamber housing thesemiconductor wafer, wherein said chamber has one or more walls with aradiation-absorbing surface.
 117. The semiconductor heating apparatus ofclaim 103, further comprising a chamber housing the semiconductor wafer,wherein said chamber has one or more walls with a radiation-reflectingsurface.
 118. The semiconductor heating apparatus of claim 117, whereinsaid chamber walls are inwardly tapered at an angle from 2 to 6 degreesfrom perpendicular.